AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 1

AVMA Guidelines for the

Humane Slaughter

of Animals: 2016 Edition

Members of the Panel on Humane Slaughter

Steven Leary, DVM, DACLAM (Chair); Washington University, St Louis, Missouri

Wendy Underwood, DVM, DACVIM (Vice Chair); Eli Lilly and Company, Indianapolis,

Indiana

Raymond Anthony, PhD (Ethicist); University of Alaska Anchorage, Anchorage, Alaska

Douglas Corey, DVM (Equine Working Group); Associated Veterinary Medical Center,

Walla Walla, Washington

Temple Grandin, PhD (Physical Methods Working Group); Colorado State University,

Fort Collins, Colorado

Sharon Gwaltney-Brant, DVM, PhD, DABVT, DABT (Noninhaled Agents Working Group);

Veterinary Information Network, Mahomet, Illinois

Robert Meyer, DVM, DACVAA (Inhaled Agents Working Group); Mississippi State University,

Mississippi State, Mississippi

Joe Regenstein, PhD (Religious/Ritual Slaughter); Cornell University, Ithaca, New York

Jan Shearer, DVM, DACAW (Animals Farmed for Food and Fiber Working Group);

Iowa State University, Ames, Iowa

Stephen A. Smith, DVM, PhD (Aquatics Working Group); Virginia-Maryland College

of Veterinary Medicine, Blacksburg, Virginia

AVMA Staff Consultants

Gail C. Golab, PhD, DVM, MANZCVS, DACAW; Chief Advocacy and Public Policy Ofﬁcer,

Advocacy and Public Policy SBU

Cia Johnson, DVM, MS; Director, Animal Welfare Division

2 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

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ISBN 978-1-882691-07-4

Version 2016.0.1

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 3

Part I—Introduction

I1.

Historical Context, Membership of the Panel,

and Notes on the Current Edition

................. 6

I2. Statement of Use ............................................... 6

I3. Evaluating Slaughter Methods .......................... 6

I4. Stress and Distress, Unconsciousness,

and Pain ............................................................ 7

I5. Animal Behavioral Considerations ................... 9

I6. Human Behavioral Considerations ................... 9

I7. References ....................................................... 10

Part II—History of Regulations, Industry

Guidance and Employee Training

in the United States

H1.

History of Regulation of Slaughter in the

United States ................................................... 11

H2. Enforcement of Humane Slaughter in the

United States ................................................... 11

H3. Auditing by Private Industry .......................12

H3.1 Clear Comments .................................... 12

H3.2 Video Auditing by Industry ................... 13

H4. References ....................................................... 13

Part III—Design of Facilities and

Slaughter Process

D1. Handling Procedures at Slaughter Plants for

Hoofstock ....................................................... 14

D1.1 Step 1—Arrival at the Plant ..................... 14

D1.1.1 Detection of Problems ......................... 14

D1.1.2 Corrective Action for Problems .......... 14

D1.2 Step 2—Unloading ................................... 14

D1.2.1 Detection of Problems ......................... 14

D1.2.2 Corrective Action for Problems .......... 15

D1.3 Step 3—Receiving .................................... 15

D1.3.1 Detection of Problems ......................... 15

D1.3.2 Corrective Actions for Problems ......... 15

D1.4 Step 4—Lairage ........................................ 15

D1.4.1 Detection of Problems ......................... 16

D1.4.2 Corrective Actions for Problems ......... 16

D1.5 Step 5—Handling System......................... 16

D1.5.1 Detection of Problems ......................... 16

D1.5.2 Corrective Actions for Handling

Problems ............................................ 17

D1.6 Step 6—Restraint ..................................... 18

D1.6.1 Detection of Problems ......................... 18

D1.7 Conditions That Cause Welfare

Problems .................................................. 19

D2. Handling

Procedures at Slaughter Plants

for Poultry ...................................................... 19

D2.1 Step 1—Electric Stunning, CAS, and

LAPS: Arrival and Lairage ........................ 19

D2.1.1 Detection of Problems ......................... 20

D2.1.2 Corrective Action for Problems .......... 20

D2.1.3 Handling and Stunning ....................... 20

D2.2 Step 2A—Birds Moved to Stunning Area

and Stunning With CAS and LAPS .......... 20

D2.2.1 CAS Live Unloading ............................ 20

D2.2.2 CAS or LAPS in Transport

Containers .......................................... 20

D2.2.3 Types of CAS and LAPS Chamber

Equipment .......................................... 20

Anesthetized on the Truck .................. 20

Drawers Moved Through a Tunnel ..... 20

LAPS System ....................................... 20

D2.2.4 Detection of Problems With CAS or

LAPS of Poultry .................................. 20

D2.2.5 Correction of Problems With CAS or

LAPS ................................................... 21

D2.3 Step 3A—Removal of Birds From CAS or

LAPS Chamber ......................................... 21

D2.4 Step 2B—Birds Moved to Stunning Area

for Electric Stunning ................................ 21

D2.4.1 Detection of Problems During

Unloading and Shackling for Electric

Stunning .............................................. 21

D2.4.2 Correction of Problems During

Unloading and Shackling For Electric

Stunning ............................................. 21

D2.5 Step 3B—Electric Stunning ...................... 21

D2.5.1 Detection of Problems During

Electric Stunning of Poultry ................ 21

D2.5.2 Correction of Problems With Electric

Stunning ............................................. 21

D3. References

..........................................................

Part IV—Techniques

T1.

Atmospheric Methods ..................................... 24

T1.1 Controlled Atmosphere .........................24

T1.1.1 CAS Design .......................................... 25

Detection of Problems ......................... 26

Corrective Action for Problems ............ 26

T1.1.2 Conclusions ......................................... 26

T1.2 Low Atmospheric Pressure ....................... 26

T1.2.1 Conclusions ......................................... 27

T2. Physical Methods ........................................ 28

T2.1 Concussive ............................................. 28

T2.1.1 Penetrating Captive Bolt Guns .......... 28

General Recommendations ............... 28

Detection of Problems ....................... 28

Corrective Action for Problems ......... 28

T2.1.2 Nonpenetrating Captive Bolt Guns ... 29

Detection of Problems ....................... 29

Corrective Action for Problems ......... 29

T2.1.3 Gunshot ............................................ 29

Basic Principles of Firearms .............. 29

Muzzle Energy Requirements ............ 30

Bullet Selection .................................. 30

Firearm Safety ................................... 31

Detection of Problems ....................... 31

Corrective Action for Problems ......... 31

Anatomic Landmarks for Use of the

Penetrating Captive Bolt and Gunshot ...32

CONTENTS

4 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

T2.2 Electric...................................................... 33

T2.2.1 Principles ............................................. 34

T2.2.2 Methods ............................................... 35

T2.2.3 Signs of Effective Stunning .................. 35

T2.2.4 General Recommendations ................. 36

Meat Quality ........................................ 36

Cattle ................................................... 36

Pigs and Small Ruminants ................... 36

Poultry ................................................. 37

T2.2.5 Detection of Problems ......................... 38

T2.2.6 Corrective Action for Problems ........... 38

T2.3 Other Physical Methods ........................... 39

T2.3.1 Decapitation ........................................ 39

T2.3.2 Cervical Dislocation ............................ 39

T3. References ....................................................... 40

Part V—Unique Species Issues

U1.

Additional Considerations: Bovine ................. 45

U1.1 Bulls .......................................................45

U1.2 Cull Cows................................................. 45

U1.3 Nonambulatory Cattle ............................. 45

U1.3.1 Downer Cow Syndrome ...................... 46

U1.3.2 The Prevention of Nonambulatory

Cattle and Downer Cow Syndrome .... 46

U1.4 Bob Veal .................................................... 46

U1.5 Fetal Effects .............................................. 47

U2. Additional Considerations: Swine .................. 47

U2.1 Nonambulatory Swine ............................. 47

U2.1.1 Preventing Nonambulatory Swine ...... 48

U3. Handling and Slaughter of Rabbits .................... 48

U3.1 Handling Procedures for Rabbits ............. 48

U4. Slaughter of Food Fish Intended for Human

Consumption ................................................. 50

U4.1 General Considerations ............................ 50

U4.2 Preparation and Environment for Food

Fish Slaughter ............................................ 50

U4.3 Methods of Slaughter for Food Fish ........ 50

Carbon Dioxide........................................ 51

Captive Bolt (Most Commonly

Nonpenetrating; One Step) ...................... 51

Gunshot .................................................... 51

Pithing ...................................................... 51

Manually Applied Blunt Force Trauma

(Cranial Concussion) Followed by

Secondary Kill Step ................................... 51

Decapitation Followed by Secondary

Kill Step ..................................................... 52

Cervical Transection Using a Knife or

Other Sharp Instrument Inserted Caudal

to the Skull to Sever the Spinal Cord and

Cervical Vertebrae, Followed by

Secondary Kill Step ................................... 52

Electrocution ............................................. 52

Exsanguination as a Secondary Kill Step .... 52

Rapid Chilling (Hypothermic Shock;

One Step or Two Step) .............................. 52

U4.4 Conclusions ............................................. 52

U5. Handling and Slaughter of Ratites ..................... 52

U6. Handling and Slaughter of Alligators ................. 54

U7. References ........................................................... 54

Part VI—Design of Facilities and Slaughter

Process for Religious Slaughter

R1. Handling Procedures at Slaughter Plants for

Hoofstock ........................................................ 59

R1.1 Step 1—Arrival at the Plant ...................... 59

R1.2 Step 2—Unloading ................................... 59

R1.3 Step 3—Receiving..................................... 59

R1.4 Step 4—Lairage ........................................ 59

R1.5 Step 5—Handling System ......................... 59

R1.6 Step 6—Restraint ...................................... 59

R1.6.1 Detection of Problems ......................... 59

R1.6.2 Corrective Action for Problems

With Restraint .................................... 59

R1.7 Step 7—Performing the Throat Cut ......... 60

R1.7.1 Detection of Problems ......................... 61

R1.7.2 Painfulness of the Cut ......................... 61

R1.7.3 Time to Lose Consciousness ............... 61

R1.7.4 Aspiration of Blood ............................. 62

R1.7.5 Corrective Action for Problems ........... 62

R2. Auditing Religious Slaughter to Improve

Animal Welfare for Both Kosher and Halal

Slaughter of Cattle, Sheep, or Goats ............... 62

R3. Auditing Religious Slaughter to Improve

Animal Welfare for Both Kosher and Halal

Slaughter of Chickens, Turkeys, and Other

Poultry ............................................................ 63

R4. The Importance of Measurement .................... 63

R5. References ....................................................... 63

CONTENTS

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 5

Introduction

In 1963, the AVMA convened the ﬁrst POE to pro-

vide guidance for veterinarians who perform or oversee

the euthanasia of animals. In 2011, the AVMA POE de-

termined there was a need to address and evaluate the

methods and agents that veterinarians may encounter

when animals are killed under conditions where meet-

ing the POE deﬁnition of euthanasia may not be pos-

sible. The guidance contained within this document

relates to the humane slaughter of animals intended for

use as food.

The content of the AVMA Guidelines for the Hu-

mane Slaughter of Animals (Guidelines) reﬂects the

AVMA’s on-going commitment to ensure that the treat-

ment of animals during every stage of life, including

during the induction of death, is as humane and re-

spectful as possible. While much remains to be learned

about animal pain and consciousness and new evidence

and technological innovation may lead to the adop-

tion of more humane techniques, this edition of the

Guidelines relies on the scientiﬁc evidence currently

available. In interpreting that evidence, the POHS was

committed to ensuring, to the best of its ability, that no

unnecessary pain or distress is inﬂicted on conscious

animals used for food prior to or during slaughter.

These Guidelines are part of a triad of documents on

humane killing—the other two being the AVMA Guide-

lines for the Euthanasia of Animals: 2013 Edition

and

the anticipated AVMA Guidelines for the Depopulation

of Animals.

The latter half of the 20th century and the ﬁrst

two decades of the 21st century have seen the prolif-

eration of the scientiﬁc study of animals’ welfare to ad-

dress public concerns regarding the ethical treatment of

animals, especially those used in biomedical research

and raised and slaughtered for food.

The treatment of

animals is an important subject for public debate and

discussion, especially in light of growing adoption of

intensive forms of agricultural and aquacultural pro-

duction and increased interest in food quality, safety,

and quantity. Additionally, the scientiﬁc community

and the public share an interest in the possibility of

substantial cognitive, emotional, psychological, and

social abilities in nonhuman species. Attention to ques-

tions about the moral status of animals has meant that

veterinarians and others have had to demonstrate to

the public due diligence in their professional roles. Ap-

proximately 10% to15% of veterinarians are involved in

promoting the health and welfare of animals that will

eventually become food.

Commensurate with increased attention to how

their meat is processed and prepared, the public has

shown greater interest in the quality of life provided for

animals raised for food, including the environments in

which they are raised, how they are handled and man-

aged, and how they are slaughtered and processed for

human consumption. Contemporary slaughter practic-

AVMA Guidelines for the Humane Slaughter

of Animals: 2016 Edition

es are considerably improved over those of times past,

but additional innovation is needed and possible. Care-

ful attention to empirical issues is essential when as-

sessing farming practices and slaughter methods from

an ethical perspective.

The POHS has worked diligently to identify and ap-

ply the best research and empirical information avail-

able to promote the humane slaughter of the species of

animals addressed in this document. Mechanical and

physical methods, electrical methods, and controlled

atmosphere and gas methods are used to bring about

unconsciousness through physical disruption, hypoxia,

neuronal depression, or epileptiform brain activity in

food animals at slaughter. A range of factors, includ-

ing expanded knowledge about the cognitive capabili-

ties of animals, technological and economic conditions,

and social and ethical considerations affecting the sus-

tainability of animal agriculture, the care and manage-

ment of food animals, and food security, will inﬂuence

the recommendations in this and future editions of this

document. The AVMA encourages its members to utilize

their scientiﬁc knowledge and practical expertise to pro-

tect and promote the health and welfare of all animals.

The Guidelines do not venture into the morality

of killing animals for food. The POHS’s focus was on

what should happen to animals when slaughter is their

ultimate fate. When animals are designated for slaugh-

ter, they should be treated with respect and handled ap-

propriately, and the slaughter process should limit the

harms experienced by these animals. Humane slaughter

methods and agents are designed to bring about rapid

loss of consciousness and, ultimately, a complete loss of

brain function in animals destined for use as food. This

means minimizing (and, where possible, eliminating)

anxiety, pain, and distress associated with terminating

the lives of the following species of animals: hoofstock

(cattle, bison, horses and mules, sheep, goats, swine,

deer, elk), poultry (chickens, turkey, pheasants, ratites,

geese, ducks), ﬁsh, alligators, and rabbits. The process

of termination, as deﬁned here, encompasses the period

from which a farmed animal designated for human food

consumption is off-loaded at a slaughter facility until it

is veriﬁed to be unconscious and, ultimately, dead and

ready for entry into the food chain.

Abbreviations

CAS Controlled atmosphere stunning

CFIA Canadian Food Inspection Agency

EEG Electroencephalography

FSIS Food Safety and Inspection Service

HMSA Humane Methods of Livestock Slaughter Act

LAPS Low-atmospheric-pressure stunning

LOP Loss of position or posture

LORR Loss of the righting reﬂex

OIE World Organisation for Animal Health

POE Panel on Euthanasia

POHS Panel on Humane Slaughter

SEP Somatosensory evoked potential

6 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

While the POHS is motivated primarily by the sci-

ence and ethics of animals’ welfare, members of the

Panel are also sensitive to adjacent concerns related to

the slaughter of animals. These include, nonexhaus-

tively, public health and safety, food safety and quality,

environmental and economic sustainability, production

adequacy and sustainability, occupational health and

impact on the labor force, international animal welfare

and trade standards, and religious and cultural expecta-

tions. These issues, however, are not the main focus of

this document. The veterinarian’s primary responsibil-

ity of doing what is in the animal’s best interest under

the circumstances (ie, using the most appropriate and

painless slaughter method possible and considering the

context of animals’ welfare in the United States) should

not be displaced by quality, quantity, or economic

arguments.

The AVMA Guidelines for the Euthanasia of Ani-

mals: 2013 Edition should be consulted if individual

animals are deemed inappropriate for the food chain.

The anticipated AVMA Guidelines for the Depopula-

tion of Animals should be consulted in the event that

a zoonotic disease, a foreign animal disease, a natural

disaster, or another concern for population health is the

issue.

I1 Historical Context, Membership of the Panel,

and Notes on the Current Edition

The membership of the POHS included consid-

erable breadth and depth of expertise in the affected

species and environments in which humane slaughter

is performed. These Guidelines represent more than 2

years’ worth of deliberation by more than 15 individu-

als, including veterinarians, animal scientists, and an

animal ethicist. In reviewing the literature and formu-

lating their recommendations, members of the Panel

tapped the expertise ofcolleagues in pertinent ﬁelds

and also received invaluable input from AVMA mem-

bers and others during a designated comment period.

The scientiﬁc integrity and practical utility of these

Guidelines are a direct result of AVMA members’ input,

as well as suggestions from others concerned about the

welfare of animals used for food and, speciﬁcally, tech-

niques used for slaughter.

In these Guidelines, methods, techniques, and

agents used to slaughter animals humanely are dis-

cussed. Illustrations, diagrams, and tables have been

included to assist veterinarians in applying their pro-

fessional judgment. Species-speciﬁc information is pro-

vided for terrestrial and aquatic species that are com-

monly farmed and slaughtered for food.

The Guidelines acknowledge that the slaughter of

animals used for food is a process involving more than

what happens to the animal at the time of its death,

and that veterinary responsibilities associated with

slaughter are not limited to the moment or procedure

of killing the animal. In addition to delineating appro-

priate methods and agents for slaughter, the Guidelines

recognize the importance of considering and applying

good preslaughter and animal-handling practices. In-

formation about conﬁrmation of death has also been in-

cluded. While some slaughter methods may be utilized

in euthanasia and depopulation, recommendations

related to euthanasia and depopulation are addressed

speciﬁcally in other documents created by their respec-

tive Panels.

I2 Statement of Use

The POHS has developed these Guidelines for use

by members of the veterinary profession who have an

interest in the humane slaughter of hoofstock, poul-

try, rabbits, alligators, and ﬁsh. The POHS’s objective

in creating the Guidelines is to provide guidance for

veterinarians about how to prevent pain and distress in

animals that have been designated for slaughter. While

we believe the Guidelines contains valuable informa-

tion that can help assure and improve animals’ welfare

during slaughter, it is important to understand that the

HMSA

and its regulations provide ﬁnal federal author-

ity regarding slaughter practices in the United States.

These Guidelines do not address methods and

techniques involved in the termination of animals

hunted for food (subsistence or otherwise) or animals

raised primarily for their fur or ﬁber.

Veterinarians experienced in the species of inter-

est should be consulted when choosing a method of

slaughter, especially for those species not covered by

the HMSA (eg, poultry, ﬁsh). To minimize distress to

animals and to prevent human injury during slaughter,

methods and agents should be selected that maintain

calm animals. Attention to species-speciﬁc anatomy,

physiology, natural history, husbandry, and behavior

will assist in understanding how various methods and

agents may impact an animal during slaughter.

Veterinarians performing or overseeing humane

slaughter should assess the potential for species-specif-

ic distress secondary to physical discomfort, abnormal

social settings, novel physical surroundings, phero-

mones or odors from previously slaughtered animals,

the presence of humans, and other factors. In evaluat-

ing slaughter methods, veterinarians should also con-

sider human safety, availability of trained personnel,

potential infectious disease concerns, conservation or

other animal population objectives, regulatory over-

sight, availability of proper equipment and facilities,

options for carcass disposal, and the potential for sec-

ondary toxicity. Human safety is of utmost importance,

and appropriate safety equipment, protocols, and ex-

pertise must be available before animals are handled.

Advance preparation of personnel must include train-

ing in the stipulated slaughter methods and assurance

of understanding of and sensitivity toward animal wel-

fare indices. Special attention should be paid to unique

species attributes that may affect how animals are

handled, stunned, and rendered unconscious. Once an

animal has been slaughtered, death must be carefully

veriﬁed. Slaughter must always be performed in ac-

cord with applicable federal, state, and local laws and

regulations.

I3 Evaluating Slaughter Methods

Some methods of slaughter require physical han-

dling of the animal. The amount of control and the kind

of restraint required will be determined not only by the

species, breed, and size of animal involved, but also

by the level of excitement and prior handling experi-

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 7

ence of the animal and competence of the personnel

performing slaughter. Proper handling is vital to mini-

mizing pain and distress in animals and to ensuring the

safety of the person performing slaughter, any bystand-

ers, and other animals that are nearby.

Selection of the most appropriate method of hu-

mane slaughter in any situation will depend on the spe-

cies and number of animals involved, available means

of animal restraint, skill of personnel, and other con-

siderations. Personnel who slaughter animals for food

must demonstrate proﬁciency in the use of the tech-

nique in a closely supervised environment. Each facility

where slaughter is performed is responsible for appro-

priately training its personnel. Experience in the hu-

mane restraint of the species of animal is critical. Train-

ing should include familiarity with the normal behavior

of the species, an appreciation of how behavior affects

handling and restraint, and an understanding of the

mechanism by which the selected technique induces

loss of consciousness and death.

Death must be veriﬁed before invasive dressing be-

gins (or before disposal of the animal for meat-quality

reasons). Personnel must be sufﬁciently trained to rec-

ognize the cessation of vital signs of different animal

species.

The POHS gave serious consideration to the fol-

lowing criteria in their assessment of the appropriate-

ness of slaughter methods: 1) ability to induce loss

of consciousness followed by death with a minimum

of pain or distress, 2) time required to induce loss of

consciousness and the behavior of the animal during

that time, especially for religious slaughter, 3) reliabil-

ity and irreversibility of the methods resulting in death

of the animal, 4) safety of personnel, 5) compatibility

with intended animal use and purpose (ie, meat con-

sumption), 6) potential psychological or emotional im-

pacts on personnel, 7) ability to maintain equipment

in proper working order, and 8) legal and religious re-

quirements.

These Guidelines do not address every contin-

gency. In circumstances that are not clearly covered by

these Guidelines, a veterinarian experienced with the

species in question should apply professional judgment

and knowledge of clinically acceptable techniques in

selecting a humane method of slaughter or euthanasia

(if required) to end an animal’s life in the best way pos-

sible. The veterinarian should consider whether 1) the

procedure results in the best outcome for the animal,

2) their actions conform to acceptable standards of

veterinary practice and are consistent with applicable

federal, state, and local regulations, and 3) the choice

of slaughter or euthanasia technique is consistent with

her or his professional obligations and ethical commit-

ment to society.

I4 Stress and Distress, Unconsciousness, and Pain

These Guidelines acknowledge that a humane ap-

proach to the slaughter of any animal is warranted,

justiﬁable, and expected by society. The overall goal

should be to minimize or eliminate anxiety, pain, and

distress prior to loss of consciousness. Therefore, both

the induction of unconsciousness and handling prior

to slaughter must be considered. Criteria for determin-

ing the humaneness of a particular slaughter method

can be established only after the mechanisms of pain,

distress, and consciousness are understood. For a more

extensive review of these issues, the reader is directed

to the AVMA Guidelines for the Euthanasia of Animals:

2013 Edition.

Humane slaughter methods produce unconscious-

ness through four basic mechanisms: 1) physical dis-

ruption of brain activity (eg, blunt cranial trauma,

penetrating captive bolt, gunshot), 2) hypoxia (eg,

controlled low atmospheric pressure for poultry, N

, Ar,

exsanguination), 3) direct depression of neurons nec-

essary for life function (eg, CO

), or 4) epilepitiform

brain activity (eg, electric stunning). Because loss of

consciousness resulting from these mechanisms can

occur at different rates, the suitability of a particular

agent or method will depend on the species and wheth-

er an animal experiences pain or distress prior to loss of

consciousness.

Distress during slaughter may be created by the

method itself or by the conditions under which the

method is applied and may manifest behaviorally (eg,

overt escape behaviors, approach-avoidance preferenc-

es [aversion]) or physiologically (eg, changes in heart

rate, sympathetic nervous system activity, hypothalam-

ic-pituitary axis activity). Stress and the resulting re-

sponses have been divided into three phases.

Eustress

results when harmless stimuli initiate adaptive respons-

es that are beneﬁcial to the animal. Neutral stress results

when the animal’s response to stimuli causes neither

harmful nor beneﬁcial effects to the animal. Distress

results when an animal’s response to stimuli interferes

with its well-being and comfort.

Although sympathetic

nervous system and hypothalamic-pituitary axis activa-

tion are well accepted as stress response markers, these

systems are activated in response to both physical and

psychological stressors and are not necessarily associ-

ated with higher-order CNS processing and conscious

experience by the animal. Furthermore, use of sympa-

thetic nervous system and hypothalamic-pituitary axis

activation to assess distress during application of CAS

methods is complicated by continued exposure during

the period between loss of consciousness and death.

Ideally, humane stunning and slaughter methods

result in rapid loss of consciousness and the associated

loss of brain function. The perception of pain is deﬁned

as a conscious experience

and requires nerve impuls-

es from peripheral nociceptors to reach a functioning

conscious cerebral cortex and the associated subcorti-

cal brain structures. The International Association for

the Study of Pain describes pain as “an unpleasant sen-

sory and emotional experience associated with actual

or potential tissue damage, or described in terms of

such damage. Activity induced in the nociceptor and

nociceptive pathways by a noxious stimulus is not pain,

which is always a psychological state, even though we

may well appreciate that pain most often has a proxi-

mate physical cause.”

Pain is therefore subjective in

the sense that individuals can differ in their perceptions

of pain intensity as well as in their physical and behav-

ioral responses to it.

Distress during administration of CO, CO

, and

the inert gases N

and Ar has been evaluated by use

8 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

of behavioral assessment and aversion testing and re-

viewed in the context of euthanasia.

It is important to

understand that aversion is a measure of preference,

and while aversion does not necessarily imply that an

experience is painful, forcing animals into aversive situ-

ations creates distress. The conditions of exposure used

for aversion studies, however, may differ from those

used for stunning or slaughter. One of the character-

istics of anesthesia in humans is the feeling that one

is having an out-of-body experience, suggesting a dis-

connection between one’s sense of self and one’s aware-

ness of time and space.

Although we cannot know for

certain the subjective experiences of animals, one can

speculate similar feelings of disorientation may contrib-

ute to the observed signs of distress with inhaled meth-

ods. In addition, agents identiﬁed as being less aversive

(eg, Ar or N

gas mixtures) can still produce overt signs

of behavioral distress (eg, open-mouth breathing) for

extended periods of time prior to loss of consciousness

under certain conditions of administration (eg, gradual

displacement).

Unconsciousness, deﬁned as loss of individual

awareness, occurs when the brain’s ability to integrate

information is blocked or disrupted. In animals, loss

of consciousness is functionally deﬁned by LORR, also

called LOP.

8,12,13

This deﬁnition is quite useful because

it is an easily observable, integrated whole-animal re-

sponse. Although any physical movement occurring

during anesthesia, euthanasia, slaughter, or depopula-

tion is often interpreted as evidence of consciousness,

cross-species data from the anesthesia literature sug-

gest that both memory formation and awareness are

abolished early in the overall process relative to loss of

reﬂex muscle activity.

Thus, vocalization and nonpur-

poseful movement observed after LORR or LOP with

properly applied CAS methods are not necessarily signs

of conscious perception by the animal. While general-

ized seizures may be observed following effective CAS

methods, these generally follow loss of consciousness;

indeed, anesthesia, coma, and generalized seizures all

represent a loss of consciousness where both arousal

and awareness in humans are low or absent.

Loss of

consciousness should always precede loss of muscle

movement.

Although measurements of brain electrical func-

tion have been used to quantify the unconscious state,

EEG data cannot provide deﬁnitive answers as to onset

of unconsciousness even when state-of-the-art equip-

ment is used. At some level between behavioral un-

responsiveness and the induction of a ﬂat EEG (indi-

cating the cessation of the brain’s electric activity and

brain death), consciousness vanishes. However, current

EEG-based brain function monitors are limited in their

ability to directly indicate unconsciousness, especially

around the transition point.

15,16

Also, it is not always

clear which EEG patterns are indicators of activation by

stress or pain.

Reduction in alpha-to-delta brain wave

ratios coincides with LOP in chickens,

18,19

reinforcing

the usefulness of LOP or LORR as an easily observable

proxy for loss of animal consciousness.

Physical methods that destroy or render nonfunc-

tional the brain regions responsible for cortical inte-

gration (eg, gunshot, captive bolt, cerebral induction

of epileptiform activity in the brain [eg, electric stun-

ning], blunt force cranial trauma, maceration) produce

instantaneous unconsciousness. When physical meth-

ods directly destroy the brain, signs of unconscious-

ness include immediate collapse (LORR or LOP) and

a several-second period of tetanic spasm, followed by

slow hind limb movements of increasing frequency.

20,21

In cattle, however, there is species variability in this re-

sponse. The corneal reﬂex will also be absent.

Signs

of effective electric stunning that induces both epilepti-

form activity in the brain and cardiac arrest are LORR,

loss of menace reﬂex and tracking of moving objects,

extension of the limbs, opisthotonos, downward rota-

tion of the eyeballs, and tonic spasm changing to clonic

spasm, with eventual muscle ﬂaccidity.

21,23

Physical

methods are inexpensive, humane, and minimize pain

if performed properly, and leave no drug residues in

the carcass. Furthermore, animals presumably experi-

ence less fear and anxiety with methods that require

little preparatory handling. However, physical methods

usually require a more direct association of the opera-

tor with the animals, which can be offensive to, and

upsetting for, the operator. Physical methods must be

skillfully executed to ensure a quick and humane death

because failure to do so can cause signiﬁcant stress, dis-

tress, and pain. Physical disruption methods are usu-

ally followed by exsanguination to ensure death and

improve meat quality. Exsanguination is also a method

of inducing hypoxia, albeit indirectly.

Controlled atmosphere stunning methods also

depress the cerebral cortical neural system, producing

loss of consciousness accompanied by LORR or LOP.

Purposeful escape behaviors should not be observed

during the transition to unconsciousness. Depending

on the speed of onset of unconsciousness, signs as-

sociated with release of conscious inhibition of motor

activity, (such as vocalization or uncoordinated muscle

contraction) may be observed at LORR or LOP. Signs

of an effective stun when the animal is in deep levels

of anesthesia include LORR or LOP, loss of eye blink

(menace reﬂex) and corneal reﬂex, and muscle ﬂaccid-

ity.

As with physical disruption methods, CAS meth-

ods are usually followed by exsanguination to ensure

death and improve meat quality.

Decapitation and cervical dislocation are physical

methods of slaughter that require separate comment.

The interpretation of brain electric activity, which can

persist for up to 30 seconds following these meth-

ods,

25–27

has been controversial.

As indicated previ-

ously, EEG cannot provide deﬁnitive answers as to the

exact onset of unconsciousness. Other studies

26,27,29–31

indicate such activity does not imply the ability to per-

ceive pain and conclude that loss of consciousness de-

velops rapidly.

In summary, the cerebral cortex or equivalent

structures and associated subcortical structures must

be functional for pain to be perceived. If the cerebral

cortex is nonfunctional because of physical disruption,

hypoxia, generalized epileptic seizure, or neuronal de-

pression, pain cannot be experienced. Motor activities

occurring following LORR or LOP, although potentially

distressing to observers, are not perceived by an uncon-

scious animal as pain or distress. Reﬂexive kicking in

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 9

unconscious animals may be mistaken for conscious

activity and can occur even after decapitation, as neu-

rologic circuits involved with walking are located in

the spinal cord.

Given that we are limited to applying

slaughter methods based on these four basic mecha-

nisms, efforts should be directed toward educating in-

dividuals involved in the slaughter process, achieving

technical proﬁciency, and reﬁning the application of

existing methods, including handling conditions prior

to slaughter.

I5 Animal Behavioral Considerations

These Guidelines are concerned with minimizing

animal distress, including negative affective or experi-

entially based states such as fear, aversion, anxiety, and

apprehension, during the slaughter process. They are

also meant to promote human well being and safety as

regards the repeated termination of animals’ lives. Vet-

erinarians and other employees conducting slaughter

should familiarize themselves with preslaughter pro-

tocols and be attentive to species and individual vari-

ability to mitigate distress in both food animals and

human handlers. The method for inducing uncon-

sciousness and the handling and restraint methods as-

sociated with it must be evaluated as an entire system.

Physical methods require more handling and restraint

of individual animals, compared with CAS, but they in-

duce instantaneous unconsciousness. Controlled atmo-

sphere stunning does not induce instantaneous uncon-

sciousness, but possible distress during handling may

be reduced. There may be a tradeoff between possible

distress during a longer time to induce unconscious-

ness and the beneﬁts of reduced handling of individual

animals.

Intentional violations of the HMSA must not be tol-

erated. Unintentional pain and/or distress at slaughter

caused by mistakes by personnel or poorly designed fa-

cilities must be addressed promptly. At all stages of the

process of termination, animals should be treated with

respect, and compromises to animal welfare should be

treated as unacceptable if not unlawful. Practitioners

and stockpersons should ensure the following:

• No conscious animal is dragged, shackled, hoisted,

or cut inappropriately. Before invasive dressing (eg,

skinning, leg removal, scalding) begins, all signs

of brainstem function, such as the corneal reﬂex,

must be abolished.

• Excessive force or frequent use of electric prods

to move animals off trucks, up and down ramps,

or into slaughter facilities or restraint devices is

avoided. Animals should not be forced to move

faster than a normal walking speed. Handlers

should move animals quietly, without using driv-

ing devices that would cause unnecessary pain

and/or distress.

• Nonambulatory or disabled animals are isolated

and moved with suitable equipment (eg, bucket of

a loader, sled) and provided appropriate veterinary

attention. Conscious nonambulatory animals must

never be dragged.

• Terrestrial animals are provided with access to wa-

ter in the lairage pens. Animals should have suf-

ﬁcient room to move in accordance with state, fed-

eral, and local statues, and pens should have room

for all the animals to lie down.

• Slaughter facilities and equipment are well main-

tained to minimize injury or pain to the animals

and employees.

• The induction of unconsciousness (eg, stunning)

causes minimal distress to the animal.

• All personnel are trained in both the application

of stunning methods and behavioral principles of

animal handling.

I6 Human Behavioral Considerations

Food animal veterinarians may be asked to bridge

the physical and psychological divide between current

practices used in the care and management of food ani-

mals and consumers by communicating the realities of

conventional food production. They may also be asked

to provide an ethical accounting and monitoring of ani-

mals’ welfare on the farm, in feedlots, in aqua-farms,

and at slaughterhouses to the public in a transparent

fashion. Food animal veterinarians are encouraged to

increase their awareness of slaughter methods and to

enhance understanding of the science behind the meth-

ods currently used with a view toward the day-to-day

complexities of managing food animals and the range

of challenges facing our contemporary food animal sec-

tor. Likewise, industry agents, veterinarians, caretak-

ers, and others engaged with the slaughter of animals

for food should be encouraged to understand the di-

versity of public concerns and trending societal values

and expectations related to how animals are farmed and

slaughtered for food.

The humane slaughter of animals is a learned skill

that requires training, respect, and self-awareness.

Personnel performing humane slaughter must be

technically proﬁcient. Periodic professional continu-

ing education on the latest methods, techniques, and

equipment available for slaughter is highly encouraged.

Personnel must also possess a temperament that does

not bolster brutality. Self-awareness when it comes to

processing animals for food will help to mitigate com-

passion fatigue and callousness.

The slaughter of individual livestock or poultry by

farm workers who are also responsible for providing

husbandry can substantially impact emotions.

There-

fore, appropriate oversight of the psychological well-

being of slaughter employees is paramount to mitigate

guilt, distress, sadness, fatigue, alienation, anxiety, and

behaviors that lack consideration of others or may lead

to harming themselves, animals, or other people. Peo-

ple may have individual differences in how they psy-

chologically react to the job of killing animals.

It is

difﬁcult to care about animals when they have to be

killed. This is called the “caring-killing paradox.”

Veterinarians and staff who are regularly exposed

to the slaughter process should also be monitored for

emotional burnout, psychological distress, or compas-

sion fatigue and be encouraged to seek appropriate

psychological counseling.

37,38

While integrating good

animal welfare in the food chain, some food animal

practitioners may be torn among serving the best in-

terest of the farmed animal, the human client (indi-

vidual), personal professional interests, and societal

10 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

concerns about improving quality of life for animals

and ensuring the availability of safe and affordable ani-

mal protein. More studies on both the impact of ani-

mal slaughter on the personnel performing it and on

attitudes toward the consumption of animals for food

among the general public will go a long way toward

promoting healthier and more respectful human–food

animal relationships.

I7 References

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AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 11

History of Regulations, Industry Guidance

and Employee Training in the United States

H1 History of Regulation of Slaughter in the United States

The Federal Meat Inspection Act of 1906 (as

amended) requires the USDA to inspect all cattle,

sheep, swine, goats, and horses brought into any plant

to be slaughtered and processed for human consump-

tion;

it does not cover poultry. Inspection of poultry

products for human consumption did not become

mandatory until passage of the 1957 Poultry Products

Inspection Act.

The 1978 HMSA made mandatory the

humane slaughter and handling of livestock in connec-

tion with slaughter of food animals in USDA-inspected

plants. Animals included under the 1978 Act are cattle,

calves, horses, mules, sheep, goats, swine, and other

livestock. Two methods of slaughter were determined

to be humane under the 1978 Act. The ﬁrst requires

that livestock be rendered insensible to pain by a sin-

gle blow or gunshot or an electrical, chemical or other

means that is rapid and effective before being shack-

led, hoisted, cast, or cut. The second method is in ac-

cordance with the ritual requirements of any religious

faith that prescribes a method of slaughter whereby the

animal suffers loss of consciousness due to ischemia

caused by the simultaneous and instantaneous sever-

ance of the carotid arteries with a sharp instrument.

Additionally, Section 1906 exempts the handling or

other preparation of livestock for slaughter under the

second method from the terms of the Act. Therefore,

the statutory requirement that livestock are rendered

insensible to pain prior to shackling, hoisting, casting,

or cutting does not apply to the handling or restraint

that is immediately associated with the cut when the

second method of slaughter is being used. Examples of

this type of slaughter include Jewish (kosher) slaughter

and Islamic (halal) slaughter.

Currently, the HMSA of 1978 does not cover poul-

try. However, some practices that promote good wel-

fare for poultry are covered by regulatory requirements

for good commercial practices.These regulations can

be found in 9 CFR Part 381.65(b) (Poultry Products

Inspection Act Regulations).

Under the Poultry Prod-

ucts Inspection Act, a poultry product is adulterated if,

among other circumstances, it is in whole, or in part,

the product of any poultry that has died by a method

other than slaughter. For example, poultry that are still

breathing on entering the scalder and die from drown-

ing and not from slaughter are considered adulterated

and unﬁt for human food and are condemned. Further-

more, in 2005, the USDA published a Federal Register

Notice (Docket No. 04-037N) on the treatment of live

poultry before slaughter. The USDA deﬁned a “system-

atic approach” as one in which establishments focus

on treating poultry in such a manner as to minimize

excitement, discomfort, and accidental injury during

the time that live poultry are held in connection with

slaughter.

Currently, this approach is voluntary on the

part of industry. A provision in the USDA appropria-

tions act for ﬁscal year 2001 (P.L. 106-387) amended

the Poultry Products Inspection Act to include manda-

tory FSIS inspection for meat from ratites and quail.

Regulations for the inspection of exotic animals

can be found under 9 CFR 352.10. The authority for

the inspection of exotic animals comes from the Agri-

culture Marketing Act of 1946 found in 7 U.S.C. 1621

et seq, which promotes distribution and marketing of

agricultural products (includes exotic species not un-

der the Federal Meat Inspection Act). Exotic animals

that are deﬁned by these regulations are reindeer, elk,

deer, antelope, water buffalo, or bison. This section

includes regulations that address humane handling

during antemortem inspection and stunning practices

to render the animals unconscious that are consistent

with the regulations pertaining to the 1978 HMSA (9

CFR 313.15 or 313.16).

Many countries have set standards for welfare prac-

tices with regard to humane slaughter, and the OIE also

includes standards for the humane conduct of slaugh-

ter in Chapter 7 of its Terrestial Animal Health Code.

The impact of such standards has just recently begun

to be felt in global trade. As an example, the Europe-

an Union’s Strategy for the Protection and Welfare of

Animals not only lays a foundation for improving wel-

fare standards in the European Union and making sure

those standards are applied and enforced in all Euro-

pean Union countries, but also expresses intent to ap-

ply equivalent welfare standards to imports from other

countries in the future.

H2 Enforcement of Humane Slaughter

in the United States

The FSIS of the USDA is tasked with the enforce-

ment of humane slaughter regulations. In the 1980s

and 1990s, enforcement of humane handling was not

a priority as FSIS focused on improving food safety

though the implementation of hazard-based inspection

systems. This was highlighted in 1997, when a survey

was conducted for the USDA.

5,6

Only three out of 10

beef plants were capable of rendering cattle uncon-

scious with a single shot from a captive bolt. The main

cause of poor captive bolt stunning was lack of mainte-

nance.

There were numerous other problems observed

in the 22 beef, pork, lamb, and veal plants that were

surveyed.

5,6

The FSIS recognized a need for improve-

ment and produced a video that served as a correlation

tool for supervisory public health veterinarians.

In 2001, Congress provided the USDA with addi-

tional funding to assist in enforcing the HMSA. This

funding enabled the FSIS to hire 17 district veterinary

medical specialists. The district veterinary medical spe-

cialist is the primary contact for humane handling and

slaughter issues in each district and serves as the liaison

between the district ofﬁce and headquarters on all hu-

mane handling matters. In addition, in February 2004,

the FSIS began tracking the amount of time inspection

program personnel spend to ensure humane handling

and slaughter requirements are met.

In February 2010, the Government Accountability

Ofﬁce published a report

that expressed concern about

uneven enforcement of humane handling and slaugh-

ter. Enforcement discrepancies were found to be greater

in small plants than in larger plants.

Following the release of that report, in April 2010,

the FSIS established a Humane Handling Enforce-

ment Coordinator position to increase the frequency

12 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

with which enforcement and inspection activities are

reviewed. The Humane Handling Enforcement Coor-

dinator coordinates the agency’s implementation and

daily enforcement of humane handling requirements

and provides professional expertise to support inspec-

tors in the ﬁeld. Additionally, in 2011, the FSIS revised

and combined older directives and notices that deﬁned

egregious animal abuse, providing ﬁeld inspectors with

clearer guidance that supports more consistent enforce-

ment.

In October 2013, the FSIS published a new guid-

ance on the systematic approach to the humane han-

dling of livestock.

Proper implementation of this guid-

ance by industry should ensure the humane treatment

of livestock presented for slaughter because the guid-

ance provides establishments with a set of practices that

will assist in minimizing excitement, discomfort, and

accidental injury. The agency will continue to improve

its guidance to ensure the best practices are implement-

ed in establishments.

Food Safety and Inspection Service inspection pro-

gram personnel perform humane handling activities on

an ongoing basis. The FSIS can, and does, take enforce-

ment actions against slaughter plants that do not com-

ply with HMSA or the regulations. The goal is to prevent

suffering of animals while protecting the food supply.

H3 Auditing by Private Industry

A scoring system that was developed for use as part

of a 1997 review became the basis of the voluntary in-

dustry guidelines published by the American Meat In-

stitute.

5,6

The ﬁrst version was published in 1997, and

the most recent complete version is by Grandin.

The

guideline considers ﬁve outcome measures. The use of

outcome-based measurements to assess animal welfare

is recommended.

11–13

Following is a summary of the ﬁve

major measurements

1. Percentage of animals rendered unconscious with

a single shot from a captive bolt or percentage of

animals where the electric stunner is placed on the

head in the correct position. The minimum accept-

able scores are 95% ﬁrst-shot efﬁcacy for captive

bolt and 99% correct positioning for electric stun-

ning.

2. Percentage of animals rendered unconscious before

hoisting to the bleed rail. To pass an audit, 100%

unconsciousness is required on a sample of 100 an-

imals. There is zero tolerance for starting invasive

procedures, such as skinning or leg removal, on an

animal showing any signs of return to conscious-

ness.

3. Percentage of cattle and pigs that remain silent

and do not vocalize (bellow, moo, or squeal) in the

stunning area. To pass an audit, 95% of the cattle or

pigs must remain silent in the stun box or conveyor

restrainer or during restraint for religious slaugh-

ter. Refer to Grandin

for more detailed informa-

tion on scoring vocalization. Vocalization scoring

should not be used for sheep.

4. Percentage of animals moved without an electric

prod. The minimum acceptable score is 75% of the

animals moved without use of an electric prod. An

excellent score is 95%.

5. Percentage of animals that remain standing and do

not fall during handling. A score of a fall is given

if the body touches the ground. Restrainer devices

that are designed to trip animals and make them

fall are not acceptable. The minimum acceptable

score is 99% handled with no falling. Falling is

scored in all parts of the facility.

Acts of abuse that should never be tolerated in-

clude, but are not limited to: 1) dragging nonambu-

latory animals; 2) beating animals; 3) poking sensi-

tive areas such as the animal’s eyes, nose, udder, or

anus; 4) deliberately driving animals over the top of

other animals; and 5) deliberately slamming gates on

animals.

In 1999, the use of this scoring system by major

meat-buying customers resulted in great improvements.

A year after McDonald’s Corporation and Wendy’s In-

ternational started using the objective scoring system,

more than 90% of beef plants were able to render 95%

of cattle unconsciousness with a single shot.

15,16

The

use of electric prods and the percentage of animals vo-

calizing were also greatly reduced.

The AVMA PHS believes that important elements

for best practice with regard to humane slaughter are:

1) maintenance logs on stunners, 2) training programs

for employees, and 3) auditing using accepted industry

auditing methodologies, such as video auditing.

In-

dividual plants can vary on the structure and elements

of their approach, so each plant will need to develop

its ownprogram. Developing best practices for humane

slaughter and handling is similar to writing a hazard

analysis and critical control points plan for food safety.

Industry assessors and auditors should conduct direct

observations to ensure that the plant employees are fol-

lowing their plant’s written program. Best practices for

humane slaughter include procedures that are done in

the plant. There should be records to show that reviews

have been conducted and that procedures are being

followed. Additional critical areas for best practice in-

clude: nonslip ﬂoors on unloading ramps and in stun

boxes, electric prod use, and handling of down, non-

ambulatory animals. Many assessors/auditors use the

American Meat Institute objective scoring system to

determine when a plant has a problem.

H3.1 CleAr Comments

When a problem is identiﬁed, it is essential that

both FSIS inspectors and private auditing companies

write clear comments describing exactly what they saw.

When return to sensibility is observed, it is essential

to not confuse corneal reﬂex, nystagmus, and natural

blinking (menace reﬂex). An animal that has a weak

corneal reﬂex after electric stunning is usually uncon-

scious, but after captive bolt or gunshot, the corneal

reﬂex must be absent. An animal that has natural blink-

ing like a live animal in the lairage is deﬁnitely sensible.

This applies to all types of stunning methods.

An example of a poor description in an inspection

report would be “rough handling.” An example of a

clear description of an abusive handling incident would

be “intentional electric prod use on sensitive mucosal

areas.” Clear comments are essential so that supervi-

sors may appropriately manage problem behavior. The

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 13

FSIS has two excellent examples of clear descriptions of

an egregious situation of inhumane handling in attach-

ments 4 and 5 of Directive 6900.2, revision 2.

H3.2 Video Auditing by industry

Two major meat companies have installed video

cameras that are monitored by a private third-party au-

diting company. The use of video auditing helps pre-

vent the problem of employees following correct proce-

dures when they are being watched and then reverting

to inappropriate methods after the inspector or auditor

is gone. Video auditing is most effective when it is done

by a third-party auditor over the Internet. Experience

has shown that internal video auditing programs are

less effective.

H4 References

1. Rawson JM. Issue brief for congress: meat and poultry inspection

issues. Updated August 27, 2002. Washington, DC: Congressio-

nal Research Service, The Library of Congress, 2002. Available

at: www.cnie.org/NLE/CRSreports/IB10082.pdf. Accessed Sep

14, 2012.

2. FSIS. Humane handling of livestock and good commercial prac-

tices in poultry. 2009. Available at: www.fsis.usda.gov/PDF/

FSRE-HH-GCP.pdf. Accessed Sep 14, 2012.

3. OIE. Chapter 7.5. Slaughter of Animals. In: Terrestrial

Animal Health Code, 2015. Available at: www.oie.int/

index.php?id=169&L=0&htmﬁle=chapitre_aw_slaughter.htm.

Accessed May 25, 2015.

4. Gavinelli A. Developments in AW policies in the EU: every-

one is responsible. Seminar of the European Institute on Ani-

mal Welfare: market-driven animal welfare in the EU and the

US. Available at: www.slideshare.net/EUintheUS/washington-

andrea-1. Accessed Jul 14, 2014.

5. Grandin T. Survey of stunning and handling in federally in-

spected beef, veal, pork, and sheep slaughter plants. Available

at: www.grandin.com/survey/usdarpt.html. Accessed Jul 14,

2014.

6. Grandin T. Objective scoring of animal handling and stunning

practices at slaughter plants. J Am Vet Med Assoc 1998;212:36–

39.

7. Government Accountability Ofﬁce. Humane methods of

slaughter act. February 2010. Available at: www.gao.gov/

assets/310/300921.pdf. Accessed Oct 17, 2012.

8. FSIS. Facilitator guide for situation-based humane handling train-

ing. Beltsville, Md: FSIS, 2011.

9. FSIS. FSIS compliance guide for a systematic approach to the

humane handling of livestock. Available at: www.fsis.usda.gov/

wps/wcm/connect/da6cb63d-5818-4999-84f1-72e6dabb9501/

Comp-Guide-Systematic-Approach-Humane-Handling-Live-

stock.pdf?MOD=AJPERES. Accessed Feb 19, 2016.

10. Grandin T, American Meat Institute Animal Welfare Commit-

tee. Recommended animal handling guidelines and audit guide: a

systematic approach to animal welfare. Washington, DC: Ameri-

can Meat Institute Foundation, 2012. Available at: www.animal-

handling.org. Accessed Aug 21, 2012.

11. Hewson CJ. Can we assess welfare? Can Vet J 2003;44:749–753.

12. Webster J. The assessment and implementation of animal wel-

fare: theory into practice. Rev Sci Tech 2005;24:723–734.

13. Whay HR, Main DCJ, Guen LE, et al. Assessment of the welfare

of dairy cattle using animal-based measurements: direct obser-

vations and investigation of farm records. Vet Rec 2003;153:197–

202.

14. Grandin T. Auditing animal welfare at the slaughter plants. Meat

Sci 2010;86:56–65.

15. Grandin T. Effect of animal welfare audits of slaughter plants

by a major fast food company on cattle handling and stunning

practices. J Am Vet Med Assoc 2000;216:848–851.

16. Grandin T. Maintenance of good animal welfare standards in

beef slaughter plants by use of auditing programs. J Am Vet Med

Assoc 2005;226:370–373.

17. FSIS. Humane handling and slaughter of livestock. Directive

6900.2, Revision 2. Washington, DC: FSIS, 2011.

14 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

Design of Facilities and Slaughter Process

D1 Handling Procedures at Slaughter

Plants for Hoofstock

d1.1 step 1—ArriVAl At tHe plAnt

The normal process is for the animals to be un-

loaded promptly after a vehicle arrives at the plant. In

the best operations, the vehicles are unloaded within

15 to 60 minutes after arrival, and industry guidelines

recommend a maximum wait time of 60 minutes.

This

requires the scheduling of an appointment between the

plant and transporter. Scheduling vehicle arrival times

prevents the problem of too many vehicles arriving at

the same time, which results in long lines and delays at

unloading. During hot weather, delayed unloading can

result in severe animal welfare problems due to heat

stress. Death losses in pigs increase as the internal tem-

perature of the trailer increases.

Figure 1 shows the

step-by-step ﬂow of animals through the plant.

D1.1.1 Detection of problems

There have been unfortunate cases where many

cattle or pigs have died while waiting an entire day to

unload. This serious problem is most likely to occur

when there is an emergency condition such as a power

failure or storm, which either shuts down the plant or

makes roads impassable.

D1.1.2 Corrective action for problems

It is best practice to have an emergency program ei-

ther to divert incoming trucks to other slaughter facili-

ties or to unload animals at auction markets, feedlots,

or fairgrounds. This will require a coordinated program

that facilitates immediate cancellation of animal load-

ing on the farm and diverts loads that are en route to

other facilities.

d1.2 step 2—unloAding

When unloading is done correctly, animals will

move off the vehicle in a quiet, orderly manner. Han-

dlers should be quiet and refrain from yelling, whis-

tling, or repeatedly hitting the sides of the vehicle. The

sound of people yelling has been shown to be very

stressful for livestock.

3,4

Electric prods can be complete-

ly eliminated during unloading of most hoofstock and

ducks. The best US sheep plants use trained sheep to

lead the animals off the vehicle.

An electric prod may

occasionally be necessary to move pigs out of a vehicle

with multiple decks. Some pigs may be very difﬁcult to

move if they have never had the experience of people

walking through their pens on the farm. Handling ex-

periences on the farm can affect pig movement in the

future.

6–8

Pigs that have become accustomed to people

walking through their pens on the farm will be easier to

move and less likely to pile up when they are handled

at the plant.

Use of electric prods on horses is strongly

discouraged; they should only be used as a last resort

when all other options have been exhausted. Accept-

able handling tools for horses include ﬂags and rattle

paddles.

D1.2.1 Detection of problems

Industry guidelines advise that if more than 1% of

animals fall during unloading or more than 5% of ani-

mals are unloaded using an electric prod, there is a wel-

fare problem in the unloading area.

10–12

Most plants can

achieve this standard, as the majority of larger plants

have banned the use of the electric prod at unloading.

There is a problem if animals in the unloading area run

into fences or pile up. Quiet handling also provides the

advantage of greatly reducing bruises,

which is an eco-

nomic incentive for the facility.

At the time of unloading, plant employees

should note whether the vehicle is overloaded. Vehi-

cles should be loaded per industry and international

guidelines.

1,9,13,14

Overloading of trucks can cause severe economic

losses. Bruised meat cannot be used for human con-

sumption. In cattle, overloading of trucks will increase

bruises, lameness, and the likelihood of nonambulatory

cattle

15–18

(for US transport regulations refer to 49 USC

Section 80502

). A large survey

in both the United

States and Canada showed that 49% of the cattle trucks

arriving at processing plants were overloaded. Cattle

that are heat stressed will breathe with their mouths

open.

Overloading trucks with pigs will increase death

losses,

and overloading horses will lead to ﬁghting,

restlessness, falling, and injury.

Research

with sheep

indicated that packing sheep too tightly on a vehicle re-

sulted in an increase in animals falling down. Animals

should also be observed for transport-induced welfare

problems such as frostbite, lacerations, heat stress, and

urine scald

Another problem that can seriously compromise

animal welfare at the slaughter plant is when the ani-

Figure 1—Step-by-step ﬂow of animals through a slaughter plant.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 15

mal is in poor condition prior to leaving the farm.

Weak, emaciated animals or severe lameness can make

humane handling difﬁcult. A survey

of 10 cattle auc-

tion markets found that 13.3% of cull dairy cows and

3.9% of cull beef cows were severely emaciated. Most

of the cows sold at these auctions go to slaughter. The

USDA does not permit the slaughter of nonambulatory

downed or emaciated cattle; however, pigs and sheep

that are not able to walk may be slaughtered. Fatigued

pigs, which are unable to walk, will recover if they are

rested. There are often big differences between produc-

ers on the percentage of fatigued pigs arriving at the

plant. Pigs fed high doses (9 mg/ton) of the growth

promotant ractopamine were harder to handle and had

more hoof problems.

26,27

Another type of animal that is extremely difﬁcult to

handle in a humane manner is the neonatal “bob veal”

dairy calf that is less than a week old. To make humane

handling possible, these calves should be properly cared

for and remain on the farm until they are old enough to

walk easily without assistance from a person.

D1.2.2 Corrective action for problems

Nonslip ﬂooring in the unloading area is essential

for all species.

10–12

Quiet handling and good welfare are

impossible if animals slip and fall. For all species (with

the possible exception of birds), a rough broom ﬁnish

is not a satisfactory nonslip ﬂoor. A rough broom ﬁn-

ish quickly wears down and becomes smooth and slick.

For cattle, bison, and other large animals, an 8 X 8-inch

(20 X 20-cm) diamond pattern with 1-inch (2.5-cm)

or deeper V grooves is recommended. For the smaller

species, such as pigs, deer, or sheep, a good ﬂoor ﬁnish

is to stamp the pattern of a 1-inch-wide-opening ex-

panded-metal mesh pattern into the concrete. There are

other suitable ﬁnishes for stamping concrete, and all of

them are rougher than a broom ﬁnish. Epoxy or grit

ﬁnishes work well for smaller species, but they will not

provide sufﬁcient traction for large animals that have

become agitated. For existing slick ﬂoors, there are

several options. In high-trafﬁc areas, such as unload-

ing ramps and scales, rubber mats made from woven

tire treads can be used. Another option is to construct a

steel grating from 1-inch-diameter steel rods welded in

a 12 X 12-inch (30 X 30-cm) square pattern.

The rods

must not be crisscrossed over the top of each other.

They must be welded into a ﬂat metal grid to prevent

the hooves from catching under the raised rods that can

cause hoof injury. Grooving tools can be rented from

a concrete supply ﬁrm for regrooving concrete. More

information on ﬂooring and the design of unloading

ramps can be found in reports by Grandin and Deesi-

and Grandin.

10,11

Meat packers should work with producers and

buyers to reduce the numbers of fatigued pigs and unﬁt

animals. Practical experience has shown that the per-

centage of fatigued pigs can be drastically reduced by

three changes in farm production practices: 1) walking

regularly through ﬁnishing pens on the farm to make

pigs calmer and easier to handle,

2) changing genetic

selection criteria to breed pigs with good leg confor-

mation, and 3) using ractopamine responsibly.

Re-

has shown that the number one welfare issue

with horses arriving at slaughter is owner neglect that

occurred on farm. Packers should clearly communicate

back to producers that the shipment of unﬁt animals is

unacceptable and implement a ﬁnancial penalty for the

practice.

d1.3 step 3—reCeiVing

For cattle, unloading areas for large trucks should

be designed with at least a 10-ft (3-m) level unloading

dock before the ramp starts.

For hogs and sheep, the

minimum acceptable level dock is 5 ft (1.5 m) long,

and for horses it is 7 ft (2.1 m).

After unloading, the

normal practice in most plants is to verify that the num-

ber of animals on the vehicle matches the paperwork.

In some plants, there is an extra handling step of weigh-

ing individual animals after unloading; however, many

plants have eliminated this by weighing the entire truck

before unloading. Weighing the entire truck has the ad-

vantage of reducing bruising of cattle.

In many pork plants, pigs are tattooed with an

identiﬁcation number as they walk off the truck. In

most other species, animal identiﬁcation is maintained

by placing the animals from each trailer in their own

pen and placing their identiﬁcation paperwork in a

holder on the fence.

D1.3.1 Detection of problems

The most likely problems that can occur during re-

ceiving is pigs piling up and falling during tattooing. For

other species, falling, piling up, or hitting fences would

be an indicator that handling needs to be improved.

D1.3.2 Corrective actions for problems

Provide nonslip ﬂooring for all species. For pigs,

redesign the tattoo area. A funnel-shaped chute will re-

sult in jamming of animals.

32,33

Plants with the calmest,

quietest pig tattooing apply a slap tattoo as pigs exit the

30-inch (76-cm) truck door side by side.

d1.4 step 4—lAirAge

This may also be called the stockyards or antemor-

tem pens. In most plants, animals are held in the same

groups that they traveled with on the trucks, which is

the ideal. In large plants, a typical lairage pen holds ei-

ther one or two entire truckloads. It is important to de-

sign the pens to hold a whole number of truckloads, as

a pen designed to hold one and a half truckloads will

invariably end up having two loads forced into it. When

new stockyards are being built, they should be laid out

so that there is one-way livestock movement through

the yards. Ideally, the unloading ramps are at one end of

the yards and the chutes to the stunner are at the other

end. One good design is to have all the animals enter the

pens from one alley and move to the stunner through

the opposite end of the pens. Designs for lairage pens

are in reports by Grandin and Deesing

and Grandin.

In smaller plants, there may be single or small groups of

animals arriving from many different owners. Animals

from each owner must either be held in their own small

pen or have physical identiﬁcation (such as eartags,

electronic identiﬁcation, or tattoo) to prevent their iden-

tiﬁcation from becoming mixed up with other animals.

The HMSA 9 CFR 313.2 (e) requires that all lai-

16 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

rage pens be equipped with water troughs, nipples or

other suitable devices so that the animals have access

to water. Well-designed and maintained lairage pens

will be free of sharp edges that can injure animals. In-

dustry recommendations for lairage pen space are 20

sq ft (1.87 m

) for cattle, 6 sq ft (0.55 m

) for market-

weight pigs, 11 to 12 sq ft (1 to 1.12 m

) for sows, 5 to

6 sq ft (0.46 to 0.55 m

) for sheep depending on size,

and 40 sq ft (3.74 m

) for mature boars.

The animals

should be provided sufﬁcient space that they can all lie

down at the same time. Before animals can be moved to

the slaughter area, they undergo antemortem inspec-

tion. After inspection, the lairage pen is tagged as ready

for processing. The exception to this rule is custom-

exempt plants, which process animals for personal use

by the owner or producer.

D1.4.1 Detection of problems

The three main problems that can occur in the lai-

rage pens are overstocking of the pens, ﬁghting between

animals causing injuries, and animals that become non-

ambulatory. Bulls are more likely to ﬁght than steers

or cows. Practical experiences with pigs have shown

that large groups (over 100 pigs) ﬁght less than small

groups. A small group of ﬁve or six pigs in a small pen

will sometimes result in prolonged ﬁghts. Bison can get

into severe ﬁghts that result in death. Another problem

is animals mounting each other, which may result in

weak animals falling down.

D1.4.2 Corrective action for problems

When ﬁghting occurs, there is usually one animal

that is the main perpetrator. This animal should be re-

moved from the group and placed in a separate pen.

Intact males of many species will often mount and ride

other animals. Ideally, bulls should be separated from

cull cows, however if animals are penned together and

bull is knocking down cull cows during mounting, he

should be removed from the pen. Similarly, ﬁghting is

a major cause of bruising in horses.

In small plants,

some of the worst ﬁghts are caused by singly raised

backyard animals that have never learned how to so-

cialize with other animals.

To prevent ﬁghting, bulls

and singly raised animals should be slaughtered within

one hour after arrival, after allowing them a minimum

of 30 minutes to calm down. When bulls are ﬁnished

for beef, they should be kept in the same groups in

which they were raised. Mixing bulls in the lairage pens

can cause meat-quality problems.

For pigs, rest in the

lairage pens after unloading for 2 to 6 hours will enable

them to recover from transport stress.

35–37

A lairage time

that is too long or no lairage time at all is detrimental to

both meat quality and welfare.

The regulations attendant to the HMSA forbid

dragging of nonambulatory animals unless they have

ﬁrst been stunned. If a nonambulatory bovine cannot

stand and walk, regulations require that it be humane-

ly euthanized. Nonambulatory pigs, sheep, and other

hoofstock may be moved to either the suspect pen

or the cripple area in the plant. In the United States,

the only acceptable methods for moving nonambula-

tory animals are sleds, skid steer loaders, or specialized

carts. In Canada, nonambulatory animals must be eu-

thanized on the trailer and cannot be moved with sleds,

skid steers, or specialized carts. The AVMA’s policy

on disabled livestock

provides recommendations for

down animals including but not limited to: Nonambu-

latory animals may be moved using a sled, mat, cart

or mechanized equipment that supports the full length

and weight of the animal. A nonambulatory animal

should not be dragged or lifted by the limbs, tail, neck

or ears.

d1.5 step 5—HAndling system

A wide variety of systems are available to move cat-

tle, pigs, and sheep from lairage pens to the place where

they are stunned or ritually slaughtered.

5,28,40

Systems

for deer and other cervids can be found in reports by

Matthews

and Haigh.

42,43

When animals area handled

correctly, they move in an orderly fashion with no fall-

ing or pileups and minimal vocalizing or use of electric

prods. During the last few minutes before slaughter, ex-

cessive use of electric prods can seriously affect meat

quality. In a study by Warner et al,

multiple shocks on

beef cattle produced tougher meat. Electric prod use in

pigs raises lactate levels,

and high lactate levels dur-

ing the last few minutes before slaughter will result in

lower pork quality.

45,46

Jamming of animals in the chute

that leads to the stunner, along with electric prod use,

will increase lactate levels.

Animals should never be

backed into the stun box.

D1.5.1 Detection of problems

Both industry guidelines and USDA FSIS regu-

lations prohibit abusive practices such as dragging

downed nonambulatory animals; poking sensitive ar-

eas such as the eyes, anus, or udder; slamming gates

deliberately on animals; deliberately driving animals

over the top of a downed animal; and beating animals.

Handling problems that compromise welfare can result

from a facility problem or an employee training issue.

Before modiﬁcations are made to a facility, employees

should be trained to use behavioral principles of live-

stock handing.

28,48

When people handle livestock in a

calm, quiet manner, design problems in the facility can

be easily located and corrected. For all species, if more

than 1% of the animals fall at any point in the facility,

there is a problem that needs to be corrected.

1,10,49

automated powered gate that causes an animal to ei-

ther fall down or be dragged along the ﬂoor is a serious

problem.

In cattle and pigs, vocalization during restraint,

handling, or painful procedures (eg, bellowing, moo-

ing, or squealing) is associated with physiologic mea-

sures of stress.

9,50–53

In two studies,

54,55

vocalization

during cattle handling and restraint at slaughter plants

was associated with obvious aversive events such as

electric prods, excessive pressure from a restraint de-

vice, and sharp edges. In other studies,

beef plants

with good handling had < 3% of the cattle vocalizing

in the stun box, restrainer, and handling in the lead-up

chute. Plants with serious problems during handling

and restraint have 25% to 32% of the cattle vocaliz-

ing in this area.

54,55,57

In a study

of pigs, high lev-

els of squealing in the stunning area were associated

with meat-quality problems. More recent research

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 17

slaughter plants shows that vocalizations in cattle are

associated with electric prod use. In well-managed beef

plants in one report,

the average percentages of cattle

moved with an electric prod with well-trained handlers

were 10% entering stun boxes and 16% entering a cen-

ter track conveyor restrainer. In plants where there

is no supervision, electric prod use can be excessive

and problematic. In another study,

electric prod use

in pigs varied greatly depending on whether a group

of pigs was easy or difﬁcult to drive. On easy-to-drive

pigs, an electric prod was used on 4% of the pigs, and

on a difﬁcult group of pigs, 20% of the pigs had to be

electrically prodded to move them into the single-ﬁle

chute.

D1.5.2 Corrective actions for handling problems

1. Crowd pens that lead to the single-ﬁle race (chute)

should not be overloaded

For pigs, cattle, bison, and many other animals, the

crowd pen that leads to the single-ﬁle chute should be

half full.

10,28,29

Cattle, pigs, deer, and bison should be

moved into the crowd pen in small, separate groups.

This principle does not apply to sheep. They should

be moved in a large, continuous group because of their

intense following behavior.

When horses are handled in a tub system, the tub

should only be half full, and the crowd gate should

never be used to push animals. For all species, handlers

should work alongside the tub and single-ﬁle chute,

and overhead catwalks should be avoided. Overﬁlling

the tub or overcrowding with the gate will cause ani-

mals to bunch up and turn back from the single-ﬁle

entry. Animals should be allowed time to move through

the system, without being rushed. When the animals

are moving through the system themselves, they should

be left alone. If the lead animal balks, allow it time to

investigate and move forward.

2. Use natural following behavior and timing of

bunches

The next group of cattle or pigs should not be

brought into the crowd pen that leads to the single-ﬁle

chute until there is space in the single-ﬁle chute. This

enables the animals to immediately enter,promotes

natural following behavior,

and prevents them from

turning around. Unlike domestic cattle and pigs, bison

often become agitated while standing and waiting in

single ﬁle; therefore, it may be best to put only one or

two bison in the single-ﬁle race at a time.

Horses arriving at auction markets and processing

plants come from a variety of backgrounds and with

various degrees of training. This can make their be-

havior more unpredictable than that of other species.

Handlers should always use caution and treat these

animals as though they are untrained. Handlers should

approach a horse on the left side, as traditionally horses

are trained to be left-side dominant. This is because

most humans are righthanded and must stand on the

left side of the horse to lead with their right hand. It is

important for horses to have visual contact with other

horses at all times until they enter the kill box. This

will aid in keeping them calm and will motivate them

to move forward as their herdmates do.

3. Teach handlers behavioral principles

Handlers need to understand behavioral principles

such as ﬂight zone and point of balance.

5,59,60

The most

common mistake when moving animals through chutes

is a handler who stands at the head of an animal and

pokes its rear in an attempt to make it move forward.

Standing in front of an animal prevents it from moving

forward. Handlers should be taught to use the move-

ment pattern shown in Figure 2.

When a person

quickly walks back past the shoulder of an animal, in

the opposite direction of desired movement, the animal

will move forward. This is an effective method for many

species.

4. Prohibit routine carrying and use of electric prods

In most plants that have adequate facilities, the

only place where an electric prod is occasionally need-

ed is at the entrance to the stun box or restrainer. The

prod should be kept in a convenient location and only

used when needed. After it is used to move the occa-

sional stubborn animal, it should be put away. Alterna-

tives, such as vibrating prods or plastic paddles, should

be the handler’s primary driving tool. A vibrating prod

can be made from a pneumatic engraving tool where

the sharp tip has been removed. A total prohibition of

electric prods is not recommended, as a single shock

from an electric prod is preferable to hard tail twisting

or hitting.

5. Use powered gates carefully

When a powered gate is used to move animals, it

should be equipped with controls that enable a person

to immediately stop its movement if an animal falls

down. Automated powered gates must be equipped

with pressure-limiting devices to prevent the gate from

either knocking animals over or dragging animals along

the ﬂoor.

6. Remove distractions that cause balking

Movement of animals through a handling facility

can often be greatly improved by making many small

changes in the facility that remove visual and aural

distractions that cause animals to balk and refuse to

move.

5,28,33,49

a. When an animal enters a stun box or restrainer,

it must not have air blowing in its face.

10,48

Figure 2—Handler movement pattern to move an animal into a

stun box or restrainer. The handler walks quickly in the opposite

direction of desired animal movement. The animal will typically

walk forward as the handler crosses the point of balance at the

shoulder.

18 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

b. Use a directional lamp to provide indirect light-

ing to light up dark chute entrances. Animals

have a tendency to move from a dark place to a

brighter place.

33,49,61

c. Eliminate reﬂections on shiny metal or wet

ﬂoors. Moving a light source may eliminate a

reﬂection on a wet ﬂoor.

Reﬂected glare from

shiny metal surfaces increases balking of cattle

in plants.

d. Cover the sides of chutes or install solid barri-

ers to prevent approaching animals from see-

ing people, vehicles, or moving machinery

ahead.

49,63

Large pieces of cardboard can be

used experimentally to determine where solid

shields are needed. The outer perimeter of a

handling facility is one of the most important

areas to cover. Cattle will remain calmer if there

is a solid barrier to prevent them from seeing

people standing close to them.

For ﬂighty spe-

cies such as deer, the use of solid sides and low

lighting will keep them calmer.

e. Animals often refuse to walk over changes in

ﬂoor type, such as moving from a concrete to a

metal ﬂoor. Pigs and cattle are also likely to balk

at shadows.

60,65

f. Reduce noise made by equipment, such as air

hissing and metal-on-metal banging and clang-

ing. Sudden intermittent sounds and move-

ments are more likely to cause agitation.

66,67

Many slaughter plants have high noise levels.

d1.6 step 6—restrAint

A list of design principles to reduce stress dur-

ing restraint follows. These principles are applicable

to conventional slaughter, which uses stunning before

bleeding, and religious slaughter.

1. Ensure pressure applied is optimal—The device

must apply enough pressure to make an animal feel

restrained, but avoid excessive pressure that will

cause struggling or vocalization. A common mis-

take is to apply additional pressure when an animal

struggles.

2. Do not trigger fear of falling—This is why nonslip

ﬂooring is so important. When devices are used

that hold an animal with its feet off the ﬂoor, the

animal must be held in a balanced, comfortable,

upright position. When a device is used that ro-

tates an animal from an upright position, the body

must be securely held and supported to prevent

struggling and slipping within the device. Re-

strainer conveyors should be equipped with a false

ﬂoor to prevent animals from seeing a visual cliff

under the restrainer,

5,70

as animals have depth per-

ception.

For conventional stun boxes where the

animal stands upright, nonslip ﬂooring is critical.

Stun boxes should never have a steeply sloped or

stepped ﬂoor; instead, a ﬂat ﬂoor is recommended.

3. Ensure smooth, steady motion of parts of the re-

straint device that contact animals—Sudden jerky

motion will cause animals to become agitated.

4. Block animals’ vision of people, moving equip-

ment, and activity on the ﬂoor—To prevent balking

and improve ease of entry into the restraint device,

animals entering the device should not be able to

see people, moving equipment, or activity on the

processing ﬂoor.

5. Ensue stun boxes are of an appropriate size—Stun

boxes must be the appropriate size for the animals

being processed. Animals must not be able to turn

around in the box.

D1.6.1 Detection of problems

Vocalization can be easily measured in plants to de-

tect problems with restrainers that are used for cattle,

horses, or pigs. Animals will vocalize if excessive pres-

sure is applied or another aversive event occurs.

54,55

Devices that have serious problems, such as excessive

pressure, will have high percentages (25% to 32%) of

the cattle vocalizing.

54,55,57,72

Well-designed and skill-

fully operated cattle restraint devices that have a head

holder will have 5% or less of animals vocalizing.

10,56

Vo-

calization scoring is not an effective assessment tool for

sheep, because they often do not vocalize in response

to painful procedures. If a horse struggles or vocalizes

while being restrained, it is often an indication that the

restraint is causing discomfort. Active head restraints

are more stressful for horses than full-body restrainers

and should be avoided.

When a restraint system is overloaded beyond its

design capacity, the use of electric prods may increase

ashandlers attempt to move animals through the plant.

The following measures can be used to assess the per-

formance of restraint devices:

1. Percentage of cattle, horses or pigs that vocalize

while entering the restraint device and while they

are held in the restraint device. The American Meat

Institute voluntary industry standard for vocaliza-

tion is 5% or less of the animals.

2. Percentage of animals (all species) that fall down to

the extent that the body touches the ground. The

voluntary industry standard is 1%

; however, the

goal should be zero.Restraint devices that trip ani-

mals or that are designed to make animals fall are

not permitted in the voluntary industry standard.

3. Percentage of animals moved with an electric

prod into the restraint device. The voluntary in-

dustry standard for cattle and pigs is ≤ 5% for

an excellent score and ≤ 25% for an accept-

able score. For sheep, the voluntary standard

for electric prod use is ≤ 5%. The OIE

recom-

mends that electric prods should not be used on

sheep, horses, or young calves. American Vet-

erinary Medical Association policy states that

“[e]lectrical devices (e.g., stock prods) should be

used judiciously and only in extreme circumstanc-

es when all other techniques have failed.”

All scores are per animal; the animal is either

moved with an electric prod or it is not. Either it is si-

lent or it vocalizes. Devices that paralyze animals using

electricity should not be used as a method of restraint.

Studies

75–78

clearly indicate that electroimmobilization

is highly aversive and should not be used. Electric im-

mobilization must not be confused with electric stun-

ning that causes unconsciousness. Animals that have

been immobilized with electricity will not be able to

vocalize to show their distress.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 19

d1.7 Conditions THAt CAuse WelfAre problems

1. Failure to provide nonslip ﬂooring—One of the

most common problems in stun boxes is slippery

ﬂoors.

When animals are continuously slipping,

they cannot stand still for stunning. Designs for

nonslip ﬂoors can be found in the section of the

document that describes unloading. Metal grating

or rubber mats work well to prevent slipping in

stun boxes.

2. Overloading equipment beyond its design capac-

ity—Two of the most common mistakes are over-

loading a single conveyor restrainer and overload-

ing of undersized CO

stunners:

a. Overloading a single conveyor restrainer. If the

goal is to have 1,000 pig carcasses/h enter the

coolerr, the restrainer will need to accommodate

1,200 live pigs/h. When pigs are forced to move

faster than 850 pigs/h in a single line, they are

moving faster than their normal walking speed.

Most large plants in which 1,000 pig carcasses/h

enter the cooler have two conveyor restrainers

with two single-ﬁle chutes and two crowd pens.

A single center-track restrainer will work well

to process 390 cattle/h if it is free of the dis-

tractions discussed previously. At 390 cattle/h,

the cattle are still moving at a normal walking

speed. For both electric prod use and vocaliza-

tion, there are few differences among different

line speeds when equipment is designed and op-

erated correctly.

b. Overloading of undersized CO

stunners. Car-

bon dioxide stunning equipment is available in

many sizes. One of the most common problems

is when a plant’s expansion causes it to outgrow

its CO

stunner. Unless the CO

stunner is re-

placed with another machine having a higher

capacity, the the following welfare problems are

likely to emerge:

i. Overloading gondolas by using electric prods

to force excess pigs to load. Pigs should have

sufﬁcient room to stand in the gondola with-

out being on top of each other.

ii. Reducing gas exposure time in an attempt to

increase the number of pigs the machine can

handle per hour. This will result in conscious

pigs emerging from the stunner.

c. Overloading single-animal stun boxes and re-

strainers. Single-animal stun boxes or restraint

boxes have a maximum speed of approximately

100 animals/h. Boxes designed to hold single

animals result in slower line speeds than than

conveyer systems, because they use a start-stop

process to put each animal in the box and then

remove it. The signs of an overloadedbox are:

i. Slamming the rear gate on animals,

ii. Increased electric prod use,

iii. More than one animal in the box for stun-

ning, and

iv. An increase in rough handling.

For all species, when the line speed exceeds 100

animals/h, the use of a conveyor system that handles

a continuous stream of animals or two or more single-

animal boxes is recommended.

3. Funnel-shaped crowd pens. Movement of pigs will

be impeded in a funnel-shaped crowd pen; there-

fore, a crowd pen that leads to a single-ﬁle chute

should have an abrupt entrance.

The entrance to

the single-ﬁle chute should be just wide enough to

allow one pig to enter. If it is too wide, two pigs

may become stuck beside each other entering the

chute. Designs for appropriate crowd pens for

cattle, sheep, and pigs may be found in publica-

tions by Grandin,

5,28,69

the Horse Welfare Associa-

tion of Canada,

and the American Sheep Industry

Association.

4. Stun boxes and single-ﬁle chutes that are too wide.

The appropriate width for stun boxes and chutes

tends to be overestimated. Stun boxes and chutes

that are too wide result in animals turning around

and becoming caught beside each other. The ap-

propriate width is 30 inches (76 cm) for cattle, 18

inches (46 cm) for market-weight pigs, 32 inches

(81 cm) for horses, 16 inches (40 cm) for sheep,

and 27 inches (70 cm) for deer. Chute width may

need to be adjusted for exceptionally large or small

animals.

5. Vertical overhead gate clearance is too low. Animals

will often refuse to walk under a vertical slide gate

or other apparatus that allows for scant clearance

or touches their back. Raising the opening height

6 inches (16 cm) will usually ﬁx this problem. On

center-track restrainers, the solid hold-down cover

may need to be raised to prevent bumping of the

animal’s shoulder when it is entering.

6. Single-ﬁle chute is too short. The single-ﬁle chute

has to be long enough that a sufﬁcient number of

animals can be held within it to allow time to re-

ﬁll the crowd pen (Table 1). The recommended

lengths should be used for systems in which ani-

mals are handled in a continuous ﬂow to the pro-

cessing line. In systems where animals are handled

rapidly in separate batches, shorter chutes (races)

can be used.

7. Animals allowed to stand in a stun box too long.

Animals should be stunned immediately after they

enter the stun box or restrainer. Holding an animal

alone in a stun box can cause isolation stress.

D.2 Handling Procedures at Slaughter Plants for Poultry

d2.1 step 1—eleCtriC stunning, CAs, And lAps:

ArriVAl And LAirAge

Poultry arrive at the plant and are weighed on a

truck scale while they are still on the vehicle. After

weighing, the poultry truck is parked in the lairage

shed with the birds still in the travel containers. The

sheds are equipped with fans and misters to keep the

Species Line speed Minimum length Maximum length

Cattle Under 25/h 20 ft (6 m) 75 ft (23 m)

Cattle 25–100/h 40 ft (12 m) 75 ft (23 m)

Cattle 200–390/h 80 ft (25 m) 200 ft (23 m)

Pigs and sheep Under 100/h 10 ft (3 m) 25 ft (7.6 m)

Pigs Over 100/h 25 ft (7.6 m) 50 ft (15 m)

Some systems with lengths longer than those recommended

here may work well.

Table 1—Recommended single-ﬁle chute lengths for cattle.

20 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

birds cool during hot weather. Holding time at the plant

should be minimized and on aveage should not be more

than six hours.

D2.1.1 Detection of problems

The most common problems encountered in poul-

try slaughter are overloaded containers, heat stress,

frost bite, and death due to exposure. Poorly main-

tained, broken containers may injure birds.

D2.1.2 Corrective action for problems

Stocking densities for travel containers have been

established through research and practical experience.

A maximum stocking density gives sufﬁcient space for

all birds to lie down without being on top of each other.

Processing plants should have an emergency plan to

care for birds in case of power failure at the plant or

natural disasters that make roads impassable. Arrange-

ments should be made so that catching and loading of

birds at the farm can be quickly cancelled before loading

is started. Loaded shipments that are already en route

should be diverted to nearby plants for processing.

D2.1.3 Handling and stunning

Three types of handling and stunning systems are

shown in Figure 3.

d2.2 step 2A—birds MoVed to Stunning AreA And

Stunning WitH CAs And lAps

D2.2.1 CAS live unloading

Controlled atmosphere stunning with live unload-

ing was one of the earliest CAS systems. In this system,

live birds in dump module containers are loaded onto a

conveyor that transports them into a gas stunning sys-

tem. This type of handling is likely less stressful than

that encountered when hanging live birds because the

birds are shackled after they are anesthetized.

D2.2.2 CAS or LAPS in transport containers

Most new CAS systems are now built as shown in

Figure 3. The birds remain in the transport containers

as they move through the system to be anesthetized.

Shackling and handling are performed after the birds

are anesthetized. There are various types of CAS or

LAPS systems where the birds are kept during stunning.

D2.2.3 Types of CAS and LAPS chamber equipment

Anesthetized on the truck

This system is used mostly with turkeys that are

transported on trucks with transport containers that

cannot be removed from the vehicle. The vehicle load-

ed with transport containers pulls into a shed; metal

panels clamp onto the side of the vehicle, and gas (CO

or N

) is blown through. As each section is anesthe-

tized, the truck is moved forward, and the next sec-

tion is stunned while the previous section is being un-

loaded. The disadvantage of this system is the need to

use a large amount of gas. Advantages include that the

system is economical to build, the system could be used

with many different types of gases, the system enables

companies to use existing transport vehicles, and birds

are not handled while conscious.

Drawers moved through a tunnel

In this system, drawers containing the chickens or

turkeys are transferred out of the racks by automated

equipment. The drawers are then transferred to a con-

veyor that moves the birds into gradually increasing

concentrations of CO

. This system uses less CO

than

the on-truck system.

LAPS system

Entire racks of dump modules, drawer modules, or

coops are rolled into a pressure vessel where the air is

slowly removed during a 3-minute cycle. An advantage

of LAPS is that it will work with all existing chicken

transport systems. It is easy to maintain, there is no ex-

pensive gas to purchase, and there is no carbon envi-

ronmental footprint. Most large chicken plants will re-

quire more than one chamber. Low-atmospheric-pres-

sure stunning must have a full electric stunner backup.

D2.2.4 Detection of problems with CAS or LAPS of poultry

Maintaining the correct gas mixtures is essential

for birds to have a smooth induction with a minimum

amount of gasping or head shaking. If the birds ﬂap

wildly and attempt to escape from the chamber, it is

not acceptable

and may indicate a problem with the

gas mixture. All chamber-type systems for either CAS

or LAPS must have either windows or video cameras

so that problems with induction can be observed. Some

discomfort during induction, such as head shaking or

gasping, may be a reasonable tradeoff to eliminate live

shackling, as live shackling is highly stressful.

81–83

It is

also essential to maintain the correct dwell times in the

Figure 3—Principles of three types of handling and stunning sys-

tems.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 21

chamber to prevent return to consciousness due to a

dwell time that is too short.

D2.2.5 Correction of problems with CAS or LAPS

Adjust gas mixtures or LAPS system to provide a

smoother induction before loss of posture. Plant man-

agement should have a monitoring procedure to visually

monitor induction and record atmospheric parameters.

The chamber should have a documented maintenance

protocol for daily, weekly, and monthly maintenance. It

is strongly recommended that all chamber-type systems

have a full electric stunner backup. This will enable a

plant to keep running if one of their chambers breaks.

In systems where there is more than one chamber,

this will prevent the temptation to run a single cham-

ber faster to temporarily replace a broken chamber. In

LAPS, speeding up the cycle would likely cause severe

stress to the animals. When plants install LAPS or CAS,

they should purchase sufﬁcient capacity so that the

chambers can be operated with the correct dwell time.

If a power failure or other malfunction occurs during

the stunning process, live birds should be immediately

removed from the chamber.

d2.3 step 3A—remoVAl of Birds From CAs

or lAps CHAmber

The palletized containers or the drawers containing

the birds are moved to the shackling area. The birds are

unconscious at this point. There are no welfare issues

unless the CAS or LAPS equipment malfunctioned.

d2.4 step 2b—birds MoVed to Stunning AreA

for EleCtriC Stunning

If a drawer system or individual coops are being

used, the drawers or coops are removed from the pal-

letized rack either manually or with use of automated

equipment. They are placed on a conveyor that runs

into the shackle room. Handlers pick up each indi-

vidual bird and hang it on the shackle line. If a dump

module system is used, a hydraulic platform operated

by an employee tilts the entire palletized container to

dump the live birds onto a conveyor that runs into the

shackle room. Handlers pick up live birds and hang

them on the shackle line. The birds are then moved by

the shackle conveyor to the water-bath stunner.

D2.4.1 Detection of problems during unloading

and shackling for electric stunning

One problem that can occur with dump modules

is unloading the birds too fast; this results in pileups

and excess birds falling off the conveyor may result in

loose birds on the premises. Broken wings are more

likely to occur in heavy birds unloaded from the dump

modules, compared with lighter birds. In drawer sys-

tems, a common problem is head entrapment. This is

caused by rough loading on the farm or poor design

of the drawer rack. Another common problem is un-

derstafﬁng of the shackle line. This results in rough

handling and employees attempting to work too fast,

which makes careful handling difﬁcult. When the

shackle line is understaffed, bruised thighs may be ob-

served because employees are slamming birds into the

shackles.

D2.4.2 Correction of problems during unloading

and shackling for electric stunning

A darkened room illuminated with blue lighting

will help keep birds calm.

Training of the employees

who operate the dumper of dump modules is essential.

This employee must learn to wait until the receiving

conveyor has space before dumping more birds. It is

also important to never shake the module to unload

birds. For heavier birds, it is strongly recommended to

install slides, conveyors, and other devices so birds do

not experience hard falls onto the conveyor. To prevent

head entrapment in drawer systems, when closing the

drawer on the farm, there should be a 1.5-inch gap be-

tween the top of the plastic drawer and the metal rack.

The live bird shackling area requires constant su-

pervision to prevent rough handling and bird abuse.

Hanging inverted on conventional shackles is stressful

to chickens

81,83

however, new designs for poultry shack-

ling systems may help reduce stress. In one design, the

breasts of the birds are supported by a horizontal mov-

ing conveyor.

In another new commercially available

system, the body of the shackled bird is supported by a

plastic device attached to the shackle.

d2.5 step 3b—eleCtriC stunning

The birds, which can be chickens, turkeys, or other

poultry, are moved to the water-bath stunner while they

are inverted and hanging by their feet on the shackle

line. The bird’s head has direct contact with the water

bath, and an electric current is passed from the water to

the leg shackle. The water bath and grounding equip-

ment must be maintained to convey a sufﬁcient elec-

tric current through the bird’s body to permit adequate

stunning and to complete the circuit.

D2.5.1 Detection of problems during electric

stunning of poultry

One of the most common problems is birds miss-

ing the stunner water bath because they are extremely

small or stunted and are mixed in with market-ready

birds. These birds are too short to have direct contact

with the water bath. Another problem is rapid return to

consciousness after stunning. This is caused by setting

the stunner amperage too low. Plant managers some-

times do this to prevent meat damage. Preshocks as

birds are entering the stunner may happen if wing tips

reach the water bath before the bird’s head is in direct

contact with the water bath. These shocks do not pro-

duce unconsciousness because they occur before the

birds enter the water bath. If both the automatic throat-

cutting machine and the backup bleeder person fail to

cut a bird’s throat, it may return to consciousness and

enter the scalder while conscious. These birds can be

easily detected after feather removal because there will

be no throat cut and the skin will be bright red. The red

skin is caused by lack of bleed out. Plant management

should strive to have 0% uncut red birds.

D2.5.2 Correction of problems with electric stunning

The height of the water-bath stunner must be ad-

justed so that the birds cannot pull themselves up and

avoid the stunner. It is also essential to avoid distrac-

tions such as people walking under the birds or doors

22 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

opening and closing near the stunner entrance. These

distractions can cause birds to pull up. The rail should

run smoothly because a bumpy ride may cause birds to

ﬂap and avoid the stunner. Preshocks can be reduced

with a well-designed entrance ramp on the stunner and

by adjusting the water level.

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24 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

Techniques

As noted in the Introduction, there are numerous

humane methods for stunning animals for slaughter

(Appendix); many of these methods are described in

the following text.

T1 Atmospheric Methods

t1.1 Controlled AtmospHere

Controlled atmosphere stunning and killing meth-

ods, also called modiﬁed atmosphere stunning or kill-

ing, produce unconsciousness, and can eventually lead

to death, by one of two basic methods: 1) by displac-

ing air and the oxygen it contains to produce O

levels

< 2% (eg, hypoxia or anoxia using inert gases such as

or Ar, or LAPS), or 2) by rapidly inducing decreased

intracellular pH and cellular function through acute hy-

percapnea (eg, CO

used either alone or together with

inert gases and supplemental oxygen to produce hyper-

capnic anoxia, hypercapnic hypoxia, or hypercapnic

hyperoxygenation). Sequential combinations of the two

methods, also called two-step or multiphase processes,

may use one gas or a mixture of gases to induce uncon-

sciousness prior to exposure to a different gas mixture

or higher gas concentration. Low-atmospheric-pressure

stunning is discussed in a separate section.

Whether a CAS method is classiﬁed as stunning

or killing depends on the amount of time the animal

remains in the modiﬁed atmosphere. Killing methods

eliminate the concern that animals may regain con-

sciousness prior to exsanguination. In either case, ani-

mals are not lifted or shackled until unconscious, such

that pain, stress, and fear associated with handling are

minimized. In addition to reducing live animal han-

dling, CAS may facilitate the ability to process a greater

numbers of animals.

As with all inhaled or atmospher-

ic methods, unconsciousness is not immediate, and any

perceived distress and discomfort by animals will vary

depending on the species, process, and gases used.

There is controversy in the scientiﬁc community

as to the optimum CAS gas mixture and conditions of

application for humane slaughter. Distress during ad-

ministration of CO

and the inert gases N

and Ar has

been evaluated by means of both behavioral assessment

and aversion testing and has been reviewed in the con-

text of euthanasia.

It is important to realize that aver-

sion is a measure of preference and that while aversion

does not necessarily imply the experience is painful,

forcing animals into aversive situations creates stress.

The conditions of exposure used for aversion studies,

however, may differ from those used for stunning or

killing. In addition, agents identiﬁed as being less aver-

sive (eg, Ar or N

gas mixtures) can still produce overt

signs of behavioral distress (eg, open-mouth breathing)

for extended time periods prior to loss of consciousness

under certain conditions of administration (eg, gradual

displacement).

A distinction must be made between immersion,

where animals are placed directly into a high concen-

tration of a gas or vapor within a container, and com-

mercial CAS processes as employed for the stunning of

poultry and pigs. Unlike immersion, in a commercial

process animals experience their introduction into CAS

atmospheres gradually, either through transport at a

controlled rate into a contained stunning atmosphere

gradient or through controlled introduction of stunning

gases into an enclosed space. The transport or introduc-

tion rate may be slow or relatively quick, depending on

the process, gases used, and speciﬁc species. Further,

denser-than-air CAS gases including CO

layer into gra-

dients within an enclosed space.

Thus, animals are not

immediately exposed to stunning conditions known to

be aversive or painful.

In studies of turkeys

and chickens,

hypoxia pro-

duced by inert gases such as N

and Ar appeared to

cause little or no aversion, where birds freely entered

a chamber containing < 2% O

and > 90% Ar. When Ar

was used to euthanize chickens, exposure to a chamber

preﬁlled with Ar, with an O

concentration of < 2%, led

to EEG changes and collapse in 9 to 12 seconds. Birds

removed from the chamber at 15 to 17 seconds failed

to respond to comb pinching. Continued exposure led

to convulsions at 20 to 24 seconds. Somatosensory-

evoked potentials were lost at 24 to 34 seconds, and the

EEG became isoelectric at 57 to 66 seconds.

With tur-

keys, immersion in 90% Ar with 2% residual O

led to

EEG suppression in 41 seconds, loss of SEP in 44 sec-

onds, and isoelectric EEG in 101 seconds, leading the

authors to conclude that exposure times > 3 minutes

were necessary to kill all birds.

Gerritzen et al

also

reported that chickens did not avoid chambers contain-

ing < 2% O

; birds gradually became unconscious with-

out showing signs of distress.

Chickens

9–12

and turkeys

killed by hypoxia show

less head shaking and open-beak breathing than birds

exposed to CO

. Respiratory disruption, deﬁned as

open-bill breathing with prolonged inspiration or pro-

longed open-bill gaping with apparent apnea or dys-

pnea, is less in anoxia-stunned birds compared with

methods combining anoxia with CO

9,13

Mandibula-

tion, the rapid open and closing of the beak, may occur

with anoxic systems, but may occur less than in other

systems.

However, broilers are noted to have more

episodes of wing ﬂapping when stunned with N

, either

alone or combined with 30% CO

, than with a two-step

process using 40% CO

, 30% O

, and 30% N

followed

by 80% CO

in air.

Failure to maintain < 2% O

when

using hypoxic or anoxic inert gas methods prolongs

survival.

15,16

In pigs, hypoxia produced by combining N

and Ar

appears to reduce, but not eliminate, aversive respons-

es. In one study,

pigs chose to place their head in a

hypoxic (< 2% O

, 90% Ar) chamber containing a food

reward, remained with their head in the chamber until

they became ataxic, and freely returned to the cham-

ber once they regained posture. In contrast, in another

study,

exposure to 90% Ar, 70% N

/30% CO

, and 85%

/15% CO

all resulted in signs of aversion, deﬁned by

the authors as escape attempts and gasping; the propor-

tion of pigs showing these behaviors was lowest with

Ar. Early removal from a hypoxic Ar or N

stunning gas

atmosphere results in rapid return to consciousness,

such that exposure times > 7 minutes are needed to en-

sure killing with these gases.

Inhalation of CO

causes acute respiratory acidosis

and produces a reversible anesthetic state by rapidly de-

creasing intracellular pH.

Both basal and evoked neu-

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 25

ral activities are depressed soon after inhalation of 100%

19–22

For pigs, exposure to 60% to 90% CO

causes

unconsciousness in 14 to 30 seconds,

19,20,23,24

with un-

consciousness occurring prior to onset of signs of exci-

tation.

22,23

For light Manchego lambs, exposure to 90%

for 60 seconds results in 100% stun,

with ob-

served levels of cortisol, epinephrine, and norepineph-

rine similar to electrically stunned animals.

A large

proportion of chickens and turkeys will enter a cham-

ber containing moderate concentrations of CO

(60%)

to gain access to food or social contact.

5,6,9

Following

incapacitation and prior to loss of consciousness, birds

in these studies show behaviors such as open-beak

breathing and head shaking; these behaviors, however,

may not be associated with distress because birds do

not withdraw from CO

when these behaviors occur.

Unlike N

and argon, which must be held within a very

tight range of concentration to produce oxygen levels

< 2%, CO

can render animals unconscious over a wide

range of concentrations, even when O

is > 2%.

Death via exposure to CO

has been described for

individual and small groups of birds.

3,28

Carbon dioxide

and its application to the humane slaughter of chick-

ens, turkeys, and ducks has been studied extensively

and has resulted in information about times to collapse,

unconsciousness and death, loss of SEPs, and changes

in EEG. Leghorn chicks 7 days of age collapsed in 12

seconds after exposure to 97% CO

Raj

found that

2 minutes’ exposure to 90% CO

was sufﬁcient to kill

day-old chicks exposed in batches. Broilers 5 weeks of

age collapsed an average of 17 seconds after entering a

tunnel ﬁlled with 60% CO

In a CAS system designed

for small ﬂock depopulation, LOP was observed in ap-

proximately 20 seconds for various ages of layers and

broilers in a 50% CO

atmosphere and approximately

30 seconds for turkeys in a 40% atmosphere.

In tests

where it took 8 seconds to achieve the target gas con-

centration, broilers and mature hens collapsed in 19 to

21 seconds at 65% CO

and 25 to 28 seconds at 35%

In a gradual-ﬁll study,

ducks and turkeys lost

consciousness before 25% CO

was reached and died

after the concentration reached 45%. At 49% CO

, EEG

suppression, loss of SEP, and EEG silence occurred in

11, 26, and 76 seconds in chickens.

In turkeys,

EEG

suppression took place in an average of 21 seconds at

49% CO

, but was reduced to 13 seconds at 86% CO

In the same report, time to loss of SEPs was not affected

by gas concentration, averaging 20, 15, and 21 seconds,

but time to EEG silence was concentration dependent

(ie, 88, 67, and 42 seconds, for 49%, 65%, and 86%

, respectively).

For humane slaughter of poultry, exposure to CO

concentrations producing a gradual induction of un-

consciousness reduces convulsions, compared with

anoxia with N

and Ar.

11,33

Practical experience in com-

mercial slaughter facilities indicates that a smooth,

gradual increase in CO

from 0% to more than 50% to

55% reduces bird reactions (eg, head shaking, open-

beak breathing) prior to LOP; chickens require a more

gradual increase in CO

concentration over time than

turkeys.

Carbon dioxide may invoke involuntary (un-

conscious) motor activity in birds, such as ﬂapping of

the wings or other terminal movements, which can

damage tissues and be disconcerting for observers.

However, wing ﬂapping is less with CO

than with N

or Ar.

13,33

A two-step or multiphase process combining

inert gases and CO

is used commercially for humane

slaughter of poultry, where birds are exposed initially to

40% CO

, 30% O

, and 30% N

, followed by 80% CO

air; the added O

during the anesthetic induction phase

has both welfare and carcass-quality advantages.

13,35,36

Thus, vocalization and nonpurposeful movement ob-

served after LORR or LOP with properly applied con-

trolled atmospheric methods are not necessarily signs

of conscious perception by the animal. While general-

ized seizures may be observed following effective CAS

methods, these generally follow loss of consciousness;

indeed, anesthesia, coma, and generalized seizures all

represent a loss of consciousness where both arousal

and awareness in humans is low or absent.

Loss of

consciousness should always precede loss of muscle

movement.

Genetics may play a role in pig CO

response vari-

ability. Panic disorder in humans is genetically linked

to enhanced sensitivity to CO

The fear network,

comprising the hippocampus, the medial prefrontal

cortex, and the amygdala and its brainstem projections,

appears to be abnormally sensitive to CO

in these pa-

tients.

The genetic background of some pigs, especial-

ly excitable lines such as the Hampshire and German

Landrace, has been associated with animals that react

poorly to CO

stunning, while calmer lines combining

the Yorkshire or Dutch Landrace conformations show

much milder reactions.

34,40

Given a choice, Duroc and

Large White pigs will tolerate 30% CO

to gain access

to a food reward, but will forego the reward to avoid ex-

posure to 90% CO

, even after a 24-hour period of food

deprivation.

17,24

A shock with an electric prod, however,

is more aversive to Landrace X Large White pigs than

inhaling 60% or 90% CO

, with pigs inhaling 60% CO

willing to reenter the crate containing CO

Until fur-

ther research is conducted, one can conclude that use

of CO

may be humane for certain genetic lines of pigs

and stressful for others.

T1.1.1 CAS design

The mechanical design of commercial CAS systems

has been reviewed by Grandin.

In open CAS systems

(Figure 4), the entry point is open to the atmosphere

with negligible concentrations of stunning gas present.

Animals are moved on continuous conveyors through

a tunnel or into a pit containing a heavier-than-air gas,

such as CO

or Ar. In a closed CAS system, batches of

animals are placed inside a chamber, and stunning gases

are introduced to the speciﬁed concentration through a

recirculating ventilation system that displaces oxygen

by the stunning gases. As with other inhaled methods,

changes in gas concentration within any enclosed space

involve two physical processes: 1) wash-in of new gas

(or washout of existing gas) and 2) the time constant

required for that change to occur within the container

for a known ﬂow rate.

42,43

Although closed systems can

potentially operate using any stunning gas, inert gases

such as N

work best in such systems because O

levels

< 2% can be achieved. This level of hypoxia is difﬁcult

to achieve in open CAS systems because N

is less dense

26 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

than air and, therefore, difﬁcult to contain. Also, closed

CAS systems use a greater volume of stunning gas than

open systems because the stunning area must be evacu-

ated prior to loading the next group of animals.

Detection of problems

Some of the most common problems are CO

con-

centration that is too low or insufﬁcient dwell time in

the chamber. These problems can result in either return

to sensibility on the slaughter line or stressful anesthetic

induction. Insufﬁcient dwell time is most likely to occur

in plants that have undersized equipment. Many CO

systems have automated powered gates to move animals

into the chamber. There is a serious problem if the au-

tomated gates either knock animals over or drag them

along the ﬂoor. If these gates cause more than 1% of the

pigs to fall, that exceeds the industry voluntary guide-

line.

If powered gates drag animals, that is a violation

of the HMSA. Another problem is overloaded gondolas

where animals do not have room to stand without being

on top of other animals. This is most likely to occur in

equipment that does not have sufﬁcient capacity.

Corrective action for problems

1. Maintain a CO

concentration of over 80%. A 90%

concentration at either the bottom of the pit or at

the ﬁnal stage of the process is strongly recom-

mended.

2. Increase dwell time if there are problems with re-

turn to sensibility.

3. Undersized equipment that has insufﬁcient capac-

ity is often the cause of insufﬁcient dwell time or

handlers overloading the gondolas with animals.

Either a larger piece of equipment or an additional

unit will be required to increase system capacity.

4. The pigs or poultry must have sufﬁcient room in

the gondolas or container to stand or lie down

without being on top of each other.

5. When automated gates are used to move pigs up

to and into the chamber, they must be equipped

with pressure-limiting devices. This prevents the

gates from knocking animals over or dragging

them along the ﬂoor. Often, powered gates work

best when they are equipped with a push button

or other control that allows the handlers to control

forward movement of the gate. When the handler

lets go of the control, the gate stops. An automated

control works well to return the gate to its start

position after it has moved the animals.

6. Ventilation problems in the plant building can

sometimes cause CO

to be sucked out of the

chamber. Some commercial CO

equipment holds

in a pit that is not sealed, and sometimes, air

pressure changes in the plant building can cause

sensible pigs or birds to emerge from the chamber.

Some of the factors that can suddenly lower CO

concentration are either turning off or turning on

large ventilation fans in the plant building, wind

blowing around the plant building, or leaving cer-

tain plant doors open. Careful observation will be

required to correct this problem. It is often cor-

rectible and no equipment purchases are required.

T1.1.2 Conclusions

For humane slaughter of poultry, initial exposure

to lower CO

concentrations and a gradual increase of

concentrations produce a smoother induction of

unconsciousness and reduce convulsions, compared

with anoxia with N

and Ar. Carbon dioxide may in-

voke involuntary (unconscious) motor activity in birds,

such as ﬂapping of the wings or other terminal move-

ments, which can damage tissues and be disconcerting

for observers; however, wing ﬂapping is less with CO

gas mixtures than with N

or Ar. For humane slaughter

of pigs, exposure to > 80% CO

is recommended.

Compared with electric stunning methods, CAS for

poultry presents some animal welfare advantages be-

cause manual handling and shackling of live birds are

eliminated. Some gas mixtures may cause unacceptable

escape behaviors, such as attempting to climb up the

sides of the container or vigorous ﬂapping in chickens

before LOP. In addition, CAS can also eliminate wel-

fare issues associated with dumping live birds from

their transport cages prior to stunning; however, this

depends on the design and implementation of CAS at

the processing plant. Controlled atmosphere stunning

for pigs and lambs may also improve animal welfare by

reducing animal handling.

t1.2 loW AtmospHeriC pressure

Low-atmospheric-pressure stunning (Figure 5) is

a recently described method for stunning birds prior

to humane slaughter. Unconsciousness due to hypoxia

occurs following a controlled and gradual reduction

of barometric pressure.

44–46

At one time the Europe-

an Union allowed the use of a vacuum chamber for

slaughter of farmed quail, partridge, and pheasant,

however this approval was revoked with the adoption

Figure 4—Animals are moved on continuous conveyors through

a tunnel (as shown) or into a pit containing a heavier-than-air gas

in open CAS systems.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 27

of EU Council Directive 1099/2009.

The method is

currently undergoing commercial testing for broiler

stunning in the United States under a USDA Ofﬁce of

New Technology Testing Approval. It is not currently

known whether the technology can be adapted for hu-

mane slaughter or depopulation of mammalian species,

such as pigs; however, the insidious effects of altitude

hypoxia on human ﬂight crew performance, including

unconsciousness, are well documented.

Low-atmospheric-pressure stunning is not rapid

decompression, as currently deemed unacceptable by

the AVMA Guidelines for the Euthanasia of Animals:

2013 Edition, but rather it is negative atmospheric pres-

sure applied gradually over time, typically over 1 min-

ute in broilers, which results in an acute hypoxic state

not unlike being in an unpressurized airplane at higher

altitudes. Maximum observed negative pressure during

commercial broiler LAPS is 23.8 in Hg (604.5 mm Hg

);

this corresponds to an atmospheric pressure of 155.5

mm Hg and an inspired Po

of 32.7 mm Hg (assuming

barometric pressure of 760 – 604.5 mm Hg = 155.5 mm

Hg X 0.21 = 32.7 mm Hg oxygen). Thus, LAPS Po

maximum negative pressure is equivalent to a 4% oxy-

gen atmosphere at sea level (32.7 mm Hg/760 mm Hg).

For comparison, the atmospheric pressure (P

) on top

of Mount Everest (elevation, approx 30,000 ft) is 225

mm Hg and the Po

is 47.3 mm Hg; at 40,000 ft, P

141 mm Hg and Po

is 29.6 mm Hg.

Rapid decompression can cause both pain and dis-

tress through expansion of gases present in enclosed

spaces.

In the case of birds, however, gases are un-

likely to be trapped in the lungs or abdomen during

LAPS owing to the unique anatomic structure of the

avian respiratory system and are thus unlikely to be-

come a source of abdominal distention. Avian lungs

are open at both ends, rigid, and attached to the ribs

and do not change size during ventilation. Attached

to the lungs are nine air sacs that ﬁll all spaces within

the thoracic and abdominal cavities. Because birds lack

a diaphragm, they move air in and out during sternal

movement using the intercostal and abdominal mus-

cles; air movement is simultaneous and continuous

with no passive or relaxed period. Thus, it is unlikely

signiﬁcant amounts of gas can be trapped within the

avian lungs or abdomen unless the trachea is blocked

for some reason.

In contrast to reports of hemorrhagic

lesions in the lungs, brain, and heart of animals under-

going rapid decompression,

no such lesions were ob-

served in birds undergoing LAPS.

No pathological evi-

dence of ear damage has been noted in LAPS birds,

and

corticosterone concentrations in LAPS-stunned broilers

were nearly one-half the levels observed in electrically

stunned birds.

The LAPS target pressure for broilers is achieved

within 1 minute from the start of the LAPS cycle and

maintained for 4 minutes 40 seconds to assure recov-

ery does not occur prior to exsanguination. Time to

ﬁrst coordinated animal movement was 58.7 ± 3.02

seconds, with light-headedness (deﬁned as time from

ﬁrst head movement to ﬁrst wing ﬂap) noted within

69.3 ± 6.37 seconds and LOP (an indicator of loss of

consciousness) occurring within 64.9 ± 6.09 seconds.

Neither mandibulation nor deep open-bill breathing

was observed in LAPS birds; bill breathing and mandib-

ulation are commonly reported during CAS stunning

with various gas mixtures.

Wing and leg paddling was

infrequent, lasting 15.1 ±1.12 seconds following LOP.

On the basis of EEG studies, increasing slow (delta)

wave activity consistent with a gradual loss of con-

sciousness occurs within 10 seconds of the start of the

LAPS cycle, peaking between 30 and 40 seconds and

coincident with LOP and ﬁrst brief movements.

The

same research group also determined that heart rate de-

creases over time during LAPS, implying minimal ad-

ditional sympathetic nervous system stimulation.

A signiﬁcant advantage of LAPS over electric stun-

ning and live-dump CAS is elimination of welfare issues

associated with dumping live birds onto the conveyor

line and elimination of manual handling and shackling

of live birds prior to electric stunning. During commer-

cial operation, birds undergoing LAPS are contained

within palletized shipping cages on transport trucks

in a holding area adjacent to the LAPS cylinders. Pal-

lets are directly loaded into the LAPS cylinders with a

fork lift. A computer in the control booth controls and

displays the status of the individual LAPS units. Low-

atmospheric-pressure stunning operations are fully au-

tomated, such that once a cycle is initiated, the load

operator cannot override or manually change the LAPS

cycle. Each LAPS cylinder has a video camera mounted

inside that can be viewed in real time on a monitor in

the control booth. Following the LAPS cycle, the pallet-

ized cages containing stunned birds are moved to the

dumping station. After dumping, the birds are moved

by conveyor belt to the shackling area prior to entry to

the processing line. As previously noted, LAPS corti-

costerone levels are lower than with electric stunning,

likely owing to elimination of live bird shackling.

T1.2.1 Conclusions

Low-atmospheric-pressure stunning produces a

quiet transition to unconsciousness without escape be-

haviors and with minimal physical activity and wing

ﬂapping. Although wing ﬂapping may be observed, it

Figure 5—The low atmospheric pressure system is used to stun

poultry via computer-controlled slow decompression. Controlled

and slow precise changes in atmospheric pressure lead to hy-

poxia from high altitude simulation and result in a loss of con-

sciousness and then irreversible stunning of the bird. This system

does not use aversive gas mixtures and eliminates the shackling

of sentient birds since birds remain in their transport containers

during the stunning process.

28 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

occurs following LOP and, therefore, consciousness.

Compared with live-dump CAS methods and electric

stunning methods, LAPS may be better from an animal

welfare standpoint because of elimination of welfare is-

sues associated with dumping live birds onto the con-

veyor line, and elimination of manual handling and

shackling of live birds prior to electric stunning. Low-

atmospheric-pressure stunning may have cost-saving

and environmental advantages over CAS in shipping

cages due to elimination of the need for gases and as-

sociated greenhouse gas emissions.

T2 Physical Methods

t2.1 ConCussiVe

T2.1.1 Penetrating captive bolt guns

Penetrating captive bolts are used for ruminants,

horses, and swine in commercial slaughter plants. Their

mode of action is concussion and trauma to the cere-

bral hemisphere and brainstem.

53–55

Properly done cap-

tive bolt stunning will instantly abolish visual evoked

potentials and SEPs from the brain.

56,57

This indicates

that the animal’s brain is no longer able to respond to a

visual or tactile stimulus because it was instantly ren-

dered unconscious. Adequate restraint is important to

ensure proper placement of the captive bolt. A cerebral

hemisphere and the brainstem must be sufﬁciently

disrupted by the projectile to induce sudden loss of

consciousness and subsequent death.

58,59

Appropriate

placement of captive bolts for various species has been

described.

54,60-64

Signs of effective captive bolt penetra-

tion and death are immediate collapse and a several-

second period of tetanic spasm, followed by slow hind

limb movements of increasing frequency.

55,58

The cor-

neal reﬂex must be absent, and the eyes must open into

a wide, blank stare and not be rotated.

55,65,66

There are two types of captive bolt guns—a pen-

etrating captive bolt with a rod that penetrates deep

into the brain and a nonpenetrating captive bolt that

is equipped with a convex mushroom head. These two

types are the most common types used in commercial

slaughter plants. Both types of captive bolts can be pow-

ered by either powder cartridges (9 mm, .22 caliber, or

.25 caliber) or compressed air. Captive bolts powered

by compressed air must be designed so that they nev-

er inject air into the brain, becasue of concerns about

contamination of the meat with speciﬁed risk materials

(neurologic).

All captive bolt guns require careful maintenance

and cleaning after each day of use. Lack of maintenance

is a major cause of captive bolt gun failure for both

powder-activated and pneumatic captive bolt guns.

Cartridges for powder-activated captive bolt guns must

be stored in a dry location because damp cartridges will

reduce effectiveness.

General recommendations

Use of the penetrating captive bolt is acceptable

for mature animals and it is the most common method

used in beef slaughter plants. It is a practical method

of humane slaughter for horses, ruminants, and swine.

Ruminants used for food should not be pithed to avoid

contamination of the carcass with speciﬁed risk materi-

als. Captive bolt guns used for larger species must have

the properly matched caliber and cartridge size. Both

penetrating and nonpenetrating captive bolts cause fo-

cal as well as diffuse injury. Injury caused by penetrat-

ing and nonpenetrating captive bolt pistols was similar

and sufﬁcient for both to be considered effective for eu-

thanasia of lambs.

On the basis of electrophysiologic

evidence,

researchers determined that the primary

determinant of effective stunning is impact of the bolt

and not penetration of the bolt into brain tissues. In

contrast, one report

credits structural changes includ-

ing focal damage adjacent to the wound track and dam-

age to peripheral tissues of the cerebrum, cerebellum,

and brainstem as the predominant factors affecting ef-

fectiveness of the stun. Both penetrating and nonpen-

etrating captive bolt guns are effective for inducing in-

stantaneous unconsciousness. Nonpenetrating captive

bolt requires more careful placement, compared with

penetrating captive bolt, to be effective.

The use of a

head restraint device is strongly recommended for non-

penetrating captive bolt. In a test on fed steers, a Jarvis

pneumatic nonpenetrating captive bolt rendered 70 out

of 75 steers instantly unconscious with a single shot.

The ﬁve failures were due to the gun being shot on an

angle that was not recommended. The nonpenetrating

captive bolt must be positioned perpendicular to the

animal’s forehead.

Detection of problems

Lack of maintenance is a major cause of captive

bolt gun failure for both powder-activated and pneu-

matic captive bolt guns.

Damp cartridges can result in

underpowered shots that are less effective. Soft-sound-

ing shots were less effective.

Studies have found that a well-trained operator can

easily render 95% or more of the animals unconscious

with a single shot from a captive bolt gun,

34,68

and ad-

vise that there is a problem if the effective ﬁrst-shot rate

falls below 95%.

The best plants have a 99% ﬁrst-shot

efﬁcacy

(FSIS has a zero tolerance policy for missed

ﬁrst shot). Results of a European study

of 8,879 cattle

skulls in two plants indicated poor precision in 4% and

3% of shot locations. Both studies show that the error

rate in captive bolt stunners is easily kept below 5%.

Corrective action for problems

1. Store cartridges for powder-activated captive bolt

guns in a dry location. Cartridges stored in a damp

location were more likely to produce ineffective

“soft” shots.

2. Minimize movement of the animal’s head. This can

be achieved with either a head-holding device or

behavioral methods such as changing lighting in

the stun box. Head holders must be used with care;

if poorly designed, they can increase cortisol levels

and balking.

In the center-track conveyor system,

the head will typically remain still without head re-

straint. This is due to having a long overhead solid

top, which prevents the animal from seeing out un-

til its feet are off the entrance ramp and it is riding

on the conveyor.

3. Head holders cannot be used on horses. Active

head restraint, where a horse’s head is clamped by

a mechanized device, should not be used. Passive

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 29

restraint, such as a tray to prevent the horse from

putting its head down, is acceptable. Passive devic-

es restrain movement without clamping the head.

4. A nonslip ﬂoor in the stun box is essential to pre-

vent slipping. Slipping causes animals to become

agitated. The stun box ﬂoor should be ﬂat or have

a slight slope. Steeply sloped or stepped ﬂoors

should not be used in stun boxes.

5. Maintain the captive bolt gun per the instructions

from the manufacturer. Captive bolt guns are preci-

sion machine tools, and daily cleaning and mainte-

nance are essential.

6. Use a test stand to determine whether the cap-

tive bolt has sufﬁcient bolt velocity. The minimum

bolt velocity is 55 m/s for steers and 70 m/s for

bulls.

55,57,75

Most captive bolt manufacturers have

test stands for their captive bolt guns.

7. For pneumatic captive bolt guns, the air compres-

sor that powers the gun must provide the air pres-

sure and volume speciﬁed by the captive bolt man-

ufacturer throughout the entire production shift.

Air accumulation tanks or an undersized compres-

sor will not provide sufﬁcient power for the gun.

8. Heavy pneumatic captive bolt guns must be hung

on a well-designed balancer so that the operator

can easily position the gun without lifting its full

weight. There are many balancer types and designs.

Balancers must be well maintained; a partially bro-

ken balancer will make it difﬁcult to position the

pneumatic captive bolt, causing the operator to ex-

ert more effort to move the gun.

9. Ergonomic design is especially important with

pneumatic captive bolt guns because they are

heavy and bulky. Small changes in handle location

or the angle that the pneumatic gun hangs on the

balancer can greatly improve ease of operation and

lessen the effort required to position the gun.

10. Switches and valves that operate gates or start and

stop conveyors must be located in a convenient

location. On a conveyor restrainer, the operator

should be able to start and stop the conveyor with-

out moving from the normal position for stunning.

11. All the valves and switches for operating convey-

ors and gates must be kept in good repair. Partially

broken hydraulic or pneumatic valves often require

excessive effort to operate.

12. In large plants that use cartridge-ﬁred captive bolt

guns, more than one gun should be available to

allow for both gun rotation and having a second

gun available if the initial shot is not effective.

Cartridge-ﬁred captive bolts are less effective when

they get too hot. Rotating the guns and allowing

hot guns to cool will prolong their useful life. If

a second stun attempt is needed, it must be per-

formed immediately to minimize pain, suffering

and distress. Plants should have a written protocol

in place for the use of the back-up stunner and sec-

ond stun attempts.

13. Orientation toward the foramen magnum is criti-

cal in calves, lambs, and kids because the head is

often rotated during restraint and a direction per-

pendicular to the skull may be too rostral, result-

ing in penetration of the frontal sinus. For adult

cattle, the gun should be placed perpendicular to

the skull to enable the bolt to hit with maximum

force.

T2.1.2 Nonpenetrating captive bolt guns

The nonpenetrating captive bolt gun has either a

wide mushroom-shaped head or a ﬂat head that does

not penetrate the brain of large mammals, such as adult

cattle, slaughter-weight pigs, sows, and adult sheep. In

general, regular nonpenetrating captive bolt guns only

stun animals. Correct positioning is critical for an effec-

tive stun of an adult cow. When a nonpenetrating cap-

tive bolt gun is used, there is little margin for error. The

stun-to-stick interval must not exceed 60 seconds. To

be effective on cows and steers, the shot must be more

accurately positioned, compared with the positioning

of a penetrating captive bolt. Nonpenetrating captive

bolts are not effective for stunning bulls, adult swine,

or cattle with long hair.

Detection of problems

Refer to the section Penetrating captive bolt guns—

Detection of problems. Be aware that the nonpenetrat-

ing captive bolt has a much smaller margin of error on

aim.

Corrective action for problems

Refer to the section Penetrating captive bolt guns—

Corrective action for problems.

T2.1.3 Gunshot

A properly placed gunshot can cause immediate

unconsciousness. Under some conditions, a gunshot

may be the only practical method of rendering animals

unconscious with extremely heavy skulls unconscious,

such as bulls, large boars, or buffalo.

Shooting should only be performed by highly

skilled personnel trained in the use of ﬁrearms and

only in jurisdictions that allow for legal ﬁrearm use.

The safety of personnel, the public, and other animals

that are nearby should be considered. For safety, a ful-

ly closed box that will contain a ricocheting bullet is

strongly recommended.

In applying a gunshot to the head for the purposes

of slaughter for captive animals, the ﬁrearm should be

aimed so that the projectile enters the brain, causing

instant loss of consciousness.

61,76–80

This must take into

account differences in brain position and skull confor-

mation between species, as well as the energy require-

ment for skull bone and sinus penetration.

53,77

Accu-

rate targeting for a gunshot to the head in various spe-

cies has been described.

77,78,81

The appropriate ﬁrearm

should be selected for the situation, with the goal be-

ing penetration and destruction of brain tissue without

emergence from the contralateral side of the head.

62,82

Basic principles of ﬁrearms

To determine whether a ﬁrearm or type of ammuni-

tion is appropriate for slaughtering animals, some basic

principles must be understood. The kinetic energy of

an object increases as the speed and weight or mass of

the object increase. In reference to ﬁrearms, the bullet’s

kinetic energy (muzzle energy) is the energy of a bul-

30 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

let as it leaves the end of the barrel when the ﬁrearm

is discharged. Muzzle energy is frequently used as an

indicator of a bullet’s destructive potential. The heavi-

er the bullet and the greater its velocity, the higher its

muzzle energy and capacity for destruction of objects

in its path.

Muzzle energy (E) can be expressed as the mass of

the bullet (M) times its velocity (V) squared, divided by

However, to accommodate units of measure com-

monly used in the United States for civilian ﬁrearms,

energy (E) is expressed in foot-pounds. This is calcu-

lated by multiplication of the bullet’s weight (W) times

its velocity in feet per second (V) squared, divided by

450,450. The International System of Units expresses

muzzle energy in joules after the English physicist

James Prescott Joule (1818 to 1889).

Representative ballistics data for various types of

ﬁrearms are provided in Table 2. The muzzle energy

of commercially available ammunition varies greatly.

For example, the difference in muzzle energy gener-

ated from a .357 magnum handgun loaded with a 180

grain compared with a 110 grain bullet may differ by as

much as 180 foot-pounds.

Velocity has an even great-

er impact on bullet energy than bullet mass. Selection

of an appropriate bullet and ﬁrearm is critical to good

performance when conducting euthanasia procedures.

Lighter-weight, higher-velocity bullets can have high

muzzle energy, but decreased penetration, which can

be an issue when penetrating thick bones.

Whereas most slaughter using ﬁrearms is conduct-

ed at close range, calculations of muzzle energy are use-

ful for determining which ﬁrearms are appropriate for

slaughter of animals of varying sizes. As the bullet trav-

els beyond the muzzle of the ﬁrearm, its energy gradu-

ally begins to decrease. While this is not a concern for

the use of ﬁrearms in close proximity to the animal,

when attempting to shoot an animal from a distance, to

ensure accuracy and that an acceptable level of muzzle

energy is achieved, a high-powered riﬂe may be the bet-

ter choice for rendering an animal unconscious. In all

cases, the most important factors in ensuring a success-

ful shot are the experience and skill of the shooter.

Muzzle energy requirements

Muzzle energy required to render animals up to

400 lb (180 kg) unconscious is a minimum of 300 ft-lb

(407 J). For animals larger than 400 lb, ﬁrearms capable

of yielding muzzle energies of 1,000 ft-lb (1,356 J) are

required for satisfactory results.

As demonstrated by Table 2, handguns do not

typically achieve the muzzle energy required to eutha-

nize animals weighing more than 400 lb (180 kg), and

therefore riﬂes must be used to render these animals

unconscious.

Some would argue that the muzzle energies recom-

mended are well beyond what is necessary to achieve

satisfactory results. Anecdotal comment suggests that

the .22 LR is one of the most frequently used ﬁrearms

to shoot livestock with varying degrees of success. Ad-

ditionally, a Canadian study

found .22 LR standard-

velocity and .22 LR high-velocity bullets failed to yield

adequate penetration of the skull.

There is little doubt

that success or failure is partially related to ﬁrearm and

bullet characteristics, but probably more so to selection

of the ideal anatomic site (ie, a site more likely to af-

fect the brainstem) for conducting the procedure. The

Humane Slaughter Association lists multiple ﬁrearms

for humane slaughter of livestock, including shotguns

(12, 16, 20, 28 and .410 gauges), handguns (.32 to .45

caliber), and riﬂes (.22, .243, .270, and .308). In gen-

eral, when comparing handguns with riﬂes, the longer

the barrel, the higher the muzzle velocity. Therefore, if

a .22 is used for humane slaughter, it is best ﬁred from a

riﬂe. The .22 should never be used on aged bulls, boars,

or rams.

To improve safety and reduce dangerous ricochet

of bullets that either pass through the animal’s head or

miss the animal, many plant managers prefer the .22 LR

despite its low muzzle energy and inability to yield ad-

equate penetration of the skull. Some may prefer to use

a pistol because it can be held closer to the head and

many people ﬁnd it easier to aim. Pistols must be larger

than a .22. There are two main differences between use

of a ﬁrearm in a slaughter plant and its use for on-farm

euthanasia. In a slaughter plant, gunshot is followed by

exsanguination, so it is not the sole agent used to cause

death. Another difference is an animal in a slaughter

plant is shot at a close range of 1 to 2 ft. (0.3 to 0.6

m). When slaughter is done in less controlled situa-

tions out on the farm, a ﬁrearm larger than a .22 LR is

recommended. It is essential to aim the shot correctly

so that the brain is penetrated. If an animal is injured

and is not rendered unconscious with a single shot, it

is sometimes much more difﬁcult to kill thereafter. The

nervous system may go into a state of arousal, and mul-

tiple shots may fail. In one case, a a gilt was shot mul-

tiple times with a captive bolt and ﬁrearm before it was

rendered unconscious.

Bullet selection

Bullet selection is quite possibly the most impor-

tant consideration for slaughter of livestock by gun-

shot. There are three basic types of bullets pertinent

to this discussion: solid points, hollow points, and

Muzzle energy

Cartridge/ﬁrearm In foot-pounds In joules

Handguns

.40 Smith and Wesson 408 553

.45 Automatic Colt Pistol 411 557

.357 Magnum 557 755

.41 Remington Magnum 607 823

10-mm Automatic 649 880

.44 Remington Magnum 729 988

Riﬂes

.22 Long Riﬂe Rim Fire 117 159

.223 Remington 1,296 1,757

30-30 Winchester 1,902 2,579

.308 2,648 3,590

30-06 Springﬁeld 2,841 3,852

Table 2—Average muzzle energies for common hand guns and

riﬂes. (Adapted from USDA, 2004, National Animal Health Emer-

gency Management System Guidelines, USDA, Washington, DC.

Available at: www.dem.ri.gov/topics/erp/nahems_euthanasia.pdf

[Accessed Aug 27, 2009] and cited by Woods J, Shearer JK, Hill

J. Recommended on-farm euthanasia practices. In: Grandin T, ed.

Improving animal welfare: a practical approach. Wallingford, Ox-

fordshire, England: CABI Publishing, 2010;194–195.)

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 31

full metal jacketed bullets. Solid-point bullets are pre-

ferred for shooting livestock since they are designed

for greater penetration of their targets. Under ideal

conditions this type of bullet will also undergo mod-

erate expansion to a mushroom shape that increases

its destructive characteristics. Hollow-point bullets

are designed with a hollowed-out tip that causes rapid

expansion and fragmentation of the bullet on impact.

The hollow-point design allows maximum transfer of

energy without risk of overpenetration. Hollow points

are less likely to richochet, but if the free bullet hits

a person, it is more dangerous than other bullets. For

applications such as slaughter plants, where it may be

desirable to control or reduce the degree of bullet pen-

etration, hollow-point bullets are preferred. However,

for the purposes of humane slaughter of livestock, the

ﬁrst requirement is that the bullet possesses sufﬁcient

energy to penetrate the skull and enter the underly-

ing brain tissue. The concern with hollow-point bul-

lets is that since the majority of their energy is released

on impact through fragmentation, they may not have

sufﬁcient energy to traverse the skull. Hollow points

would be safer in a slaughter plant, but they may need

to be used with a larger ﬁrearm than would solid points.

The other extreme is represented by full metal jacket

bullets, which do not expand or fragment on impact

with their targets. These bullets have a lead core with

a thin metal jacket cover that completely covers (sur-

rounds) the bullet. Full metal jacket bullets generally

achieve maximum penetration, which may have ben-

eﬁts for humane slaughter but also creates additional

safety hazards for bystanders. Full metal jackets are not

recommended in slaughter plants because of safety is-

sues. Shotguns loaded with shot shells (No. 4, 5, or 6 or

slugs) have sufﬁcient energy to traverse the skull but,

unlike bullets from either a handgun or a riﬂe, rarely

exit the skull. These are important considerations when

selecting a ﬁrearm for humane slaughter. Probably the

most important point to be made relative to the use of

gunshot for humane slaughter is that scientiﬁc infor-

mation on ﬁrearm and bullet selection is lacking. There

is an urgent need for research for best animal welfare.

Firearm safety

Firearm safety cannot be overemphasized. Guns

are inherently dangerous and must be handled with

caution at all times. This needs to be the mindset in

handling and use of ﬁrearms. Common recommenda-

tions include 1) assume that all ﬁrearms are loaded, 2)

always know where the muzzle is and never allow it

to point in the direction of oneself or bystanders, 3)

keep ﬁngers away from the trigger and out of the trig-

ger guard until ready to ﬁre, 4) be sure of the target and

what lies beyond it, 5) always be sure that the gun is un-

loaded when not in use, and 6) keep the safety on until

ready to ﬁre. To improve safety, many managers prefer a

single-shot riﬂe with either a bolt or break-open action.

The action remains open until the operator is ready to

ﬁre. For those desiring more information or training on

proper use of ﬁrearms, readers are advised to contact lo-

cal hunter safety programs. These programs offer train-

ing in ﬁrearm safety and also provide information on

rules and regulations for ﬁrearm use.

Firearms should never be held ﬂush to an animal’s

body. The pressure within the barrel when ﬁred may

cause the barrel of the gun to explode, placing the

shooter and observers at great risk of injury. Ideally, the

muzzle of the ﬁrearm should be held within 1 to 2 ft (30

to 60 cm) of the animal’s forehead and perpendicular to

the skull with the intended path of the bullet roughly in

the direction of the foramen magnum. This will reduce

the potential for ricochet while directing the bullet to-

ward the cerebrum, midbrain, and medulla oblongata,

which will assure immediate loss of consciousness and

rapid death.

When other methods cannot be used, an accu-

rately delivered gunshot is acceptable for humane

slaughter.

78,87,88

When an animal can be appropriately

restrained, the penetrating captive bolt, preferably one

designed for euthanasia, is preferred to a gunshot be-

cause it is safer for personnel. Prior to shooting, ani-

mals accustomed to the presence of humans should be

treated in a calm and reassuring manner to minimize

anxiety. In the case of wild animals, gunshots should be

delivered with the least amount of prior human contact

necessary.

Detection of problems

A well-trained shooter can render 95% or more

of the animals insensible with a single shot. There is a

deﬁnite problem if the ﬁrst-shot efﬁcacy rate falls below

95%.

Safety is a major concern with ﬁrearms with a

free bullet when they are used in a slaughter plant. Use

of a ﬁrearm that is not sufﬁciently powerful is a com-

mon cause of failure of the ﬁrst shot.

Corrective action for problems

1. Minimize movement of the animal’s head. Refer to

the section Penetrating captive bolt guns—Correc-

tive action for problems.

2. A nonslip ﬂoor in the stun box is essential to pre-

vent slipping. Slipping causes animals to become

agitated.

3. The ﬁrearms must be taken apart and fully cleaned

each day. The gun should be replaced when it be-

comes worn out. Some ﬁrearms are not designed

for heavy continued shooting in a large slaughter

plant. For each particular ﬁrearm, plant manage-

ment needs to determine a schedule for replace-

ment. Firearms in need of replacement should be

returned to a licensed dealer.

4. Switch and valves: refer to the section Penetrating

captive bolt guns—corrective action for problems.

5. Two people should be used to move and shoot frac-

tious or otherwise difﬁcult-to-handle animals such

as bison and ﬂighty animals such as horses or deer.

One person moves the animal into the kill box or

restrainer, and the other shoots the animal. This

makes it possible for the animal to be shot before it

has an opportunity to become agitated.

6. If the ﬁrst shot fails to render the animal instan-

taneously unconsciousness, a second stun attempt

must be performed immediately to minimize pain,

suffering and distress. Plants should have a written

protocol in place for the use of the back-up stunner

and second stun attempts.

32 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

Anatomic landmarks for use of the penetrating captive

bolt and gunshot

In bovines, the point of entry of the projectile

should be at the intersection of two imaginary lines,

each drawn from the outside corner of the eye to the

center of the base of the opposite horn (Figure 6a).

Alternatively in long faced cattle or young-stock, a

point on the midline of the face that is halfway be-

tween the top of the poll and an imaginary line con-

necting the outside corners of the eyes can be used

(Figure 6b).

Firearms should be positioned so that

the muzzle is perpendicular to the skull to avoid rico-

chet.

The location for placement of a captive bolt for en-

try of a free bullet or shooting goats is illustrated in

Figure 7. The optimal position is approximately 1 ½

inches (3.8 cm) behind (toward the back of the head)

an imaginary line connecting the outside corners of the

eyes with the projectile directed toward the back of the

throat. An alternate site may be determined by using the

intersection of two imaginary lines, each drawn from

the outside corner of the eye to the center of the base of

the opposite ear with the projectile directed toward the

back of the throat.

The location for placement of a cap-

tive bolt or entry of a free bullet for shooting of sheep is

illustrated in Figure 8. The optimal position for horn-

less sheep is the top of the head on the midline.

alternate site is the frontal region.

For heavily horned

sheep, the optimal site is behind the poll aiming toward

the angle of the jaw.

There are three possible sites for shooting swine:

frontal, temporal, and from behind the ear toward the

opposite eye (Figure 9).

The frontal site is in the cen-

ter of the forehead slightly above a line drawn between

the eyes. The projectile should be directed toward the

Figure 6—Anatomic site for gunshot or placement of a captive

bolt and desired path of the projectile in cattle. The point of entry

of the projectile should be at the intersection of two imaginary

lines, each drawn from the outside corner of the eye to the cen-

ter of the base of the opposite ear (A). Alternatively in long faced

cattle or young-stock (B), a point on the midline of the face that

is halfway between the top of the poll and an imaginary line con-

necting the outside corners of the eyes can be used. (Adapted

with permission from Shearer JK, Nicoletti P. Anatomical land-

marks. Available at: www.vetmed.iastate.edu/vdpam/extension/

dairy/programs/humane-euthanasia/anatomical-landmarks. Ac-

cessed Jun 24, 2011.)

Figure 7—Anatomic sites for gunshot or placement of captive

bolts and desired path of the projectile in goats. The optimal po-

sition is determined by using the intersection of two imaginary

lines, each drawn from the outside corner of the eye to the cen-

ter of the base of the opposite ear with the projectile directed

toward the back of the throat. (Adapted with permission from

Shearer JK).

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 33

spinal canal. The temporal site is slightly anterior and

below the ear.

The correct anatomic site for application of gun-

shot and penetrating captive bolt for equids is illustrat-

ed in Figure 10.

The site for entry of the projectile is

described as being on the intersection of two diagonal

lines, each running from the outer corner of the eye to

the base of the opposite ear.

t2.2 eleCtriC

Electric stunning for humane slaughter causes im-

mediate loss of consciousness.

59,92

Alternating current

has been used to euthanize dogs, cattle, sheep, goats,

swine, chickens, foxes, mink, and ﬁsh.

55,76,80,92–101

When

done correctly, electric stunning produces grand mal

seizures, which have a tonic (rigid) action followed by

clonic (paddling) action. These seizures occur prior to

the electric transmission of pain stimuli to the CNS, so

the procedure is not painful or distressful.

To produce the grand mal seizure, electrodes must

Figure 8—For polled sheep (A), the proper site is at or slightly

behind the poll aiming toward the angle of the jaw (ie, base of the

tongue). Alternatively, a site high on the forehead aiming toward

the foramen magnum (or spinal canal; B) or aiming toward the

angle of the jaw or base of the tongue may be used. (Adapted

with permission from Shearer JK, Nicoletti P. Anatomical land-

marks. Available at: www.vetmed.iastate.edu/vdpam/extension/

dairy/programs/humane-euthanasia/anatomical-landmarks.

Accessed Jun 24, 2011.)

Figure 9— There are three possible anatomic sites for gunshot

and penetrating captive bolt application in swine: frontal, tempo-

ral and from behind the ear toward the opposite eye. The frontal

site is in the center of the forehead slightly above a line drawn

between the eyes. The bolt or bullet should be directed toward

the spinal canal. The temporal site is slightly anterior and below

the ear. The ideal target location and direction of aim may vary

slightly according to breed and the age of the animal (due to

growth of the frontal sinuses). (Adapted with permission from

Shearer JK, Nicoletti P. Anatomical landmarks. Available at:

www.vetmed.iastate.edu/vdpam/extension/dairy/programs/hu-

mane-euthanasia/anatomical-landmarks.Accessed Jun 24, 2011.)

34 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

be placed so that the current goes through the brain.

102

For stunning poultry, the current reaching the brain

must be adequate to produce an epileptic seizure but

less than that required for cardiac ﬁbrillation leading to

death.

103

In poultry, epileptic activity in the brain may

require less current than that required for cardiac ﬁ-

brillation and death.

103

In mammals, reliable induction

of an epileptic seizure may require a greater amount

of current than that required for induction of cardiac

arrest.

104

If killing is not performed quickly, then con-

sciousness is regained.

105

T2.2.1 Principles

Ohm’s law involves current, potential difference

(ie, resistance), and frequency. Current, or what ﬂows

through a wire, is measured in terms of amps (A). Cur-

rent is proportional to the potential difference across

two points. Voltage (V) is a measure of that difference

in electric potential between two points in a wire. Re-

sistance, which determines how much current will ﬂow,

is measured in terms of ohms. Power, or current multi-

plied by voltage, is measured in watts (W). Frequency,

or the number of cycles per second, is measured in

hertz (Hz).

When electric stunning is used for humane slaugh-

ter, appropriate electric parameters must be used. These

parameters vary with species and size. The effectiveness

of electric stunning, in general, increases with increas-

ing current and decreasing frequency. A minimum of

1.25 A is required for market-weight pigs,

41,106,107

1.00 A

for sheep,

and 1.25 A for cattle.

106

Amperage must be

maintained for at least 1 second. Insufﬁcient amperage

can cause an animal to be paralyzed without losing in-

sensibility.

107

Electronic equipment designed to provide

constant amperage, which sets the amperage and allows

voltage to vary according to animal resistance, may pre-

vent amperage spiking.

107,108

Older voltage-regulated

electronic units allow changes in amperage (spiking),

which may cause injury and blood spotting.

The minimum current required to induce an epi-

leptic response depends on the stunning frequency.

Unconsciousness is most effectively induced at a fre-

quency of 50 cycles (50 Hz).

98,109

Plant managers will

often use higher frequencies to reduce damage to the

meat caused by petechial hemorrhages (blood spot-

ting). It is generally accepted that higher frequencies

(800 Hz or greater) do not result in better stunning.

In fact, the duration of clonic-tonic seizures increases

with higher stunning frequencies and incurs a delay in

Figure 10—Anatomic site for the application of gunshot or pen-

etrating captive bolt for equids. The point of entry of the projectile

should be at the intersection of two imaginary lines, each drawn

from the outside corner of the eye to the center of the base of the

opposite ear. (Adapted with permission from Shearer JK, Nicoletti

P. Anatomical landmarks. Available at: www.vetmed.iastate.edu/

vdpam/extension/dairy/programs/humane-euthanasia/anatomical-

landmarks. Accessed Jun 24, 2011.)

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 35

time to unconsciousness. Animals stunned using high-

er frequencies will regain sensibility more quickly.

110

other studies,

98,107,111

frequencies of 2,000 to 3,000 Hz

failed to induce unconsciousness. Grandin

107

recom-

mends that higher frequencies only be used when they

are passed through at least two electrodes to the head.

Frequenices of sine waves at 1,592 Hz or square waves

at 1,642 Hz are effective in pigs, but the period of un-

consciousness will be shorter.

110

Eight hundred hertz

applied to the head with 50 Hz applied to the body is

also acceptable.

112

Proper electric stunning must not be confused with

electric immobilization that paralyzes an animal with-

out inducing unconsciousness.

113

Immobilization with-

out unconsciousness is highly aversive and must not be

used.

114,115

Electrocution induces death by cardiac ﬁbril-

lation, which causes cerebral hypoxia.

99–101

However, an-

imals do not lose consciousness for 10 to 30 seconds or

more after onset of cardiac ﬁbrillation. It is imperative

that animals be unconscious before being electrocuted.

T2.2.2 Methods

Three methods are used to perform electric stun-

ning: the head-only reversible method; the one-step

head-to-body cardiac arrest method; and the two-step

method consisting of a current applied only to the head,

followed by a current applied to the body, which stops

the heart.

116

The head-only method does not cause car-

diac arrest and will result in a return to consciousness

in 15 to 30 seconds.

59,117

In the head-only method, ani-

mals should be bled within 15 seconds.

117

Tongs must

be placed so that the current goes only through the

head, which can be accomplished by placing tongs ei-

ther on both sides of the head or on the top and bottom

of the head (Figure 11).

The one-step method uses current applied through

the head to the body to induce cardiac arrest. Current is

simultaneously passed through both the brain and the

heart, which induces cardiac ﬁbrillation and immedi-

ate loss of consciousness (Figure 12).

59,116

Wotton and

Gregory

118

suggest that the induction of cardiac arrest

provides a major animal welfare advantage because it

promotes the start of death. Use of the head-to-body (or

–chest, -back) method has been shown to be highly ef-

fective in inducing irreversible unconsciousness in over

98% of pigs evaluated.

Pork plants using V-shaped con-

veyor restrainers have achieved > 99% correct electrode

placement when the one-step head-to-body cardiac ar-

rest method is used.

119

Grandin

108

recommends when

the one-step method is used that the ﬁrst 1-second

treatment should be at least 1.25 A at 50 to 60 Hz. One

electrode must be placed on the head, and the other

electrode can be placed on any part of the body (except

for sensitive areas such as the eye, ear, or rectum). The

ﬁrst electrode must not be placed on the neck or the

back of the neck because the current will bypass the

brain and cause instant pain.

The two-step method (Figure 13) uses the head-

only method followed by a second application of the

tongs to the chest. This method causes unconscious-

ness ﬁrst and then death by cardiac arrest. Applying the

second current by placing the electrode on the chest

behind the foreleg has been reported to be effective.

120

T2.2.3 Signs of effective stunning

Unconsciousness occurs when electricity inhibits

impulses from both the reticular activating and the so-

matosensory systems of the brain.

121

Signs of effective

seizure induction include extension of the legs, opis-

thotonus, and downward rotation of the eyeballs as

Figure 11—Proper electrode placement for the head-only electric

stun method.

Figure 12—Proper electrode placement for the one-step (head-

to-body) electric stun method, where the current is passed si-

multaneously through both the brain and the heart. The head

electrode may be placed on the forehead or immediately behind

the ear (as shown).

36 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

well as epileptic seizures or the clonic tonic syndrome

described above. The presence of an epileptic state has

been considered to be a guarantee of an effective elec-

tric stun.

59,106

On a more practical level, signs of effective stun-

ning have been described.

Although the legs may

move, it is the head that must be examined when the

animal is hung on the rail after the rigid phase of the

epileptic seizure stops. The head and neck should be

limp and ﬂoppy, and the tongue should hang out. Sheep

heads may not hang directly straight down because of

anatomic differences, but pig and cattle heads should

hang straight down. If natural blinking occurs, the

animal is not stunned. Nystagmus may occur in elec-

tric stunning especially when frequencies > 50 Hz are

used. Rhythmic breathing must cease and vocalizations

should not occur. Gasping is permissible after electric

stunning, but it must not be confused with rhythmic

breathing where the animal’s ribs move in and out. Ani-

mals electrically stunned with the head only method

will start to recover when kicking stops.

T2.2.4 General recommendations

Electric stunning requires special skills and equip-

ment that will ensure passage of sufﬁcient current

through the brain to induce loss of consciousness and

tonic and clonic epileptic spasms. Unconsciousness

must be induced before cardiac ﬁbrillation or simul-

taneously with cardiac ﬁbrillation. Cardiac ﬁbrillation

must never occur before the animal is rendered uncon-

scious. One-step methods that apply electric current

from head to tail, head to foot, or head to moistened

metal plates on which the animal stands are unaccept-

able because they often bypass the brain. The two-step

method should be used in situations where there may

be questions about sufﬁcient current to induce a grand

mal seizure with tonic and clonic spasms. This ap-

proach enables observation of tonic and clonic spasms

before a second current is applied to induce cardiac ar-

rest. Electroimmobilization that paralyzes an animal

without ﬁrst inducing unconsciousness is extremely

aversive and is unacceptable.

114,115

For both humane

and safety reasons, the use of household electric cords

is not acceptable.

Meat quality

The head-only method has both animal welfare

and meat-quality issues.

Negative meat effects include

decreased tenderness, increased drip-loss (water-bind-

ing capacity; synersis leading to water puddling), and

pale muscle color due to more intense muscular con-

tractions compared with either one-step or two-step

cardiac arrest stunning. Plant management may be

tempted to lower the amperage and increase frequency

to reduce blood splash (petechial hemorrhages) and

broken backs. Stunner settings that reliably induce epi-

leptic activity in the brain must be used.

Cattle

A two-step electric stun method must be used with

grown cattle

107,122

owing to the large size of this spe-

cies. Current must be applied to the head to induce un-

consciousness before a second current is applied to the

body to induce cardiac arrest.

123

Because grown cattle

are so large, the head must be properly restrained be-

fore afﬁxing electrodes ﬁrmly to the head. A frequency

of 50 to 60 Hz should be used for the stun

107

if head-

only stunning is used. A 3-second application of 1.15 A

at 50 cycles applied between the nose and the neck is

effective to induce epileptiform activity in the brain.

124

Pigs and small ruminants

In the interest of animal welfare, electric stunning

of sheep should be done with an amperage of at least

1.0 A (160 V), and in pigs, a minimum of 1.25 A should

be used for 100-kg (220-lb) animals.

106,125

In the United

States, market-weight pigs are much heavier, and more

amperage may be required to reliabily induce uncon-

sciousness in these animals. Pigs weighing 130 kg (287

lb) live weight require 1.8 to 2.0 A.

126

More recent re-

search has shown that amperage is the most important

electric parameter,

127

but the use of a single electric pa-

rameter such as amperage is not sufﬁcient to guarantee

effective stunning.

128

Plant operators should also evalu-

ate the animals for signs of a grand mal seizure using

the methods described by Grandin.

The time between stunning and bleeding is criti-

cal when head-only stunning is used. Animals should

be bled within 15 seconds.

59,129

When cardiac arrest

is induced, the animals should be bled within 60 sec-

onds. Most large commercial plants use head-to-body

stunning where the current is passed simultaneously

through both the brain and the heart.

34,116

In small

plants, Grandin

119

has observed problems with animals

Figure 13—Proper electrode placement for the two-step electric

stun method. First a current is passed from the nose plate to

stanchion bars on the neck, causing unconsciousness. This is fol-

lowed by the application of a second current from the neck stan-

chion to the brisket electrode, causing death via cardiac arrest.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 37

returning to consciousness after head-only stunning

because of slow hoisting procedures. To prevent return

to consciousness, a second current should be applied

to the body immediately after initial head stunning to

stop the heart.

120

Proper restraint is critical to allow the

correct placement of the electrodes. Electrodes should

be cleaned daily and properly maintained.

Improper electric stunning of sheep and pigs

can cause blood splash, pale muscle color, or broken

bones. These problems are a meat-quality issue and

not an animal welfare concern because passage of the

current through the brain has already induced uncon-

sciousness. The tongs or wand should be pressed ﬁrmly

against the animal before the current is turned on. If the

wand is energized before it is ﬁrmly applied, pigs will

produce a short squeal but sheep will remain silent.

This is a welfare concern because the animal would feel

the shock. When the wand or tong is only partially ap-

plied, the animal does not receive the full amount of

current.

130

Electric stunners work best when they are

equipped with an automatic timer.

Poultry

Electric stunning is the most universally accepted

and used method for stunning prior to slaughter for

poultry.

103

The most widely used method for electros-

tunning poultry is the electric water-bath stunning

method (Figure 14), which involves the direct contact

of the bird’s head in an electriﬁed water bath. Birds

are shackled and, while suspended upside down, pass

through a water bath. Each bird is immediately stunned

for a period that lasts between 30 and 60 seconds.

131

Efﬁcacy of the water-bath system is inﬂuenced

by the species, number, and size of the birds passing

through the water bath because with increasing size

and number of birds in the bath at one time the resis-

tance increases and because parallel paths of current

arise with increasing numbers of birds. Variable resis-

tance can result in insufﬁcient current to produce im-

mediate unconsciousness. Constant-current stunners

may alleviate this problem.

132

Smaller commercial facilities may use a handheld

stunner for electrically stunning birds. When this

method is used, birds must be properly restrained and

held. Electrodes must be properly constructed to en-

sure contact with skin through the bird’s feathering.

Placing water on the head of the bird reduces resistance

and enhances the stunning process.

Welfare issues for electric stunning of poultry ex-

ist. Birds must be handled carefully, as the shackling

procedure may be distressful and painful.

133

If wing

ﬂapping occurs immediately prior to the entrance of

the water-bath stunner, preshocks from the stunner

can occur.

134

Breast rubs, low lighting, and a smooth

transition into the stunner can reduce the frequency

of wing ﬂapping. Proper stunner design, including a

nonconductive entrance, will also help eliminate pres-

tun shocks. Shackles must be of the appropriate size

for the species and speciﬁc birds. If handheld stunners

are used, then appropriate placement of the electrodes

between the ears and eyes is essential. Because of the

variable resistance between species, ﬂocks, and even

individual birds, recommendations for optimal electric

parameters for effective stunning in poultry are difﬁ-

cult to make

135

United States model—Contrary to the European

model, electrical stunning in the United States involves

pulsed direct current with low current (25 to 45 mA/

bird),

103

low voltage (10 to 25 V),

103,136,137

and high fre-

quency (approx 500 Hz).

103,136,137

This type of system

became possible with advances in electrical circuitry

and changes to the length of the water bath cabinet that

increase dwell time of the birds and decrease the total

resistance in the water bath.

103

In a survey of 329 US

poultry plants, 92.1% reported using electrical stun-

ning and 77.4% of those plants used low-voltage (10 to

25 V), high-frequency (500 Hz) systems.

121

beHAViorAl reACtions

Efﬁcacy of the stunning in US slaughter plants has been

determined by assessing corneal and comb reﬂexes.

121

Typically, a bird is considered stunned by plant person-

nel when it becomes unresponsive to stimulation of

the cornea or comb with its eyes wide open, an arched

neck, and tucked wings.

121

One study

138

evaluated a

2-phase step-up stunner, with a ﬁrst phase consisting

of low-voltage (12 and 15 V), high-frequency (550

Hz) pulsed direct current for 10 seconds and a second

phase consisting of sinusoidal wave alternating current

(50 Hz at 40, 50, and 60 V for 5 seconds).

138

The best

results for this combination occurred in male birds at

the highest voltage settings (phase one, 15 V; phase

two, 60 V).

137

Under these conditions, only 22% of the

birds had corneal reﬂexes, 18% had spontaneous blink-

ing, and < 10% had wing ﬂapping.

138

pHysiologiC reACtions

One study

138

that evaluated a 2-phase step-up stunner,

with a ﬁrst phase consisting of low-voltage (12 and 15

V), high-frequency (550 Hz) pulsed direct current for

10 seconds and a second phase consisting of sinusoi-

dal wave alternating current (50 Hz at 40, 50, and 60

V for 5 seconds), found that 45% of the birds did not

achieve an isoelectric EEG. Contradicting this, another

research group evaluating a similar 2-phase step-up

stunner (phase one, 23 V [550 Hz direct current for 10

seconds]; phase two, 15 V [60 Hz alternating current

for 5 seconds]) found that the poststunning EEG had

a brief period of high-amplitude spikes that progres-

sively decreased in amplitude over time.

These inves-

tigators found the EEG recording of the brain activity

to be very similar to that seen with the European model

of electrical stunning.

summAry

Results of studies of birds stunned with the low-voltage

US model indicate that the birds are unresponsive to

Figure 14—In electrical water-bath stunning, birds are shackled,

and while suspended upside down, the bird’s head comes into

direct contact with an electriﬁed water bath.

38 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

stimuli. However, the physiologic data are contradic-

tory and it is unclear whether birds truly reach a state

of unconsciousness. As noted by others,

138,139

further

research is needed to evaluate the effectiveness and hu-

maneness of electrical stunning with low voltage set-

tings in 1- and 2-phase stunning systems.

ConClusions

The biological variability of birds makes it difﬁcult to

construct recommendations for optimal parameters for

electrical stunning of poultry at slaughter. Inadequate

electrical variables can result in a return to conscious-

ness before birds enter the neck slitter. However, use of

electrical frequencies that are too high results in an in-

crease in blood spotting,

131

leading to larger amounts of

carcass waste and an overall increase in the number of

birds needed to yield the same amount of end product.

T2.2.5 Detection of problems

Failure to cause immediate unconsciousness is

highly stressful and may be painful. Humans experience

pain when electroconvulsive shock therapy fails.

140

Sev-

eral causes of electric stunning failure have been noted.

The most common causes of return to consciousness

after any type of electric stunning are incorrect elec-

trode placement and poor bleeding.

118,119

Another cause

of failure that has been noted in cattle and pigs is dehy-

dration of the animal prior to stunning.

116

And ﬁnally,

poor equipment maintenance can also cause failures in

the procedure.

Another common cause of failure to induce uncon-

sciousness is incorrect placement of the electrodes.

121

Electrodes must never be placed on eyeballs, ears or

other sensitive areas of the body. Likewise, electrodes

must not be placed on wet metal plates on which the

animal stands. Experiments with dogs showed that

electrode positions where the brain is bypassed do not

cause instantaneous unconsciousness. When electricity

passes only between the forelimbs and hind limbs or

neck and feet, it causes the heart to ﬁbrillate but does

not induce sudden loss of consciousness.

The animal

will be electrocuted, but will remain conscious until it

dies from cardiac ﬁbrillation.

Four options are available for correct electrode

placement for the head-only method, including on both

sides of the head between the eye and ear, the base of the

ear on both sides of the head, and diagonally below one

ear and above the eye on the opposite side of the head.

For cattle, neck to nose is effective.

123,124

For the one-

step (head-to-body) method, the head electrode may be

placed on the forehead or immediately behind the ear.

The head electrode should never be placed on the neck

because the brain will be bypassed.

119

Diagonal move-

ment of the electric current through the body can be

accomplished by placing the head electrode behind one

ear and the body electrode on the opposite side. An-

other position that is effective is head to back.

116

When

the two-step procedure is used, placement of the body

electrode behind the forelimb is effective.

120

Electrodes

consisting of a metal band or chain around the nose and

a band or chain around the thorax appear to be effective

for pigs weighing up to 125 kg (275.6 lb).

141

Grandin

119

states that energizing the electrodes

prior to placement should not be done because pigs

will squeal, possibly because of poor electrode con-

tact. However, when the electrode is energized after it

is ﬁrmly applied, the pig will not squeal.

119

When the

electrodes are applied to the temporal fossae of a sheep’s

head, they can be stunned multiple times with no in-

crease in either heart rate or glucose secretion.

142

This

indicates that the sheep does not remember being re-

peatedly shocked.

Even when electric methods that stop the heart

are used, there are a few animals where cardiac arrest

is not induced. This is the reason why good bleeding

technique is essential.

119

The most common cause of

return to sensibility after head-only stunning is a stun-

to-bleed interval of > 15 seconds.

When electric methods are used, the following

signs of return to consciousness must be absent: rhyth-

mic breathing, righting reﬂex, vocalization, natural

eyeblink (menace reﬂex), and tracking of a moving ob-

ject.

120

There are deﬁnite problems with electric stun-

ning if pigs squeal or cattle moo or bellow when the

electrodes are applied.

Vocalization cannot be used in

sheep because sheep often do not vocalize when they

are in pain. A well-trained operator should be able to

place the electrodes in the correct position on 99% or

more of the animals. There is a problem if more than

1% of the cattle or pigs vocalize during electrode ap-

plication.

89,119

Proper equipment maintenance is essential. At a

minimum, electrodes should be cleaned once daily and

regularly maintained.

107

Old, worn, or rusted equip-

ment should be replaced on a regular schedule.

T2.2.6 Corrective action for problems

1. Check to ensure that the electric stunner is in-

ducing a grand mal epileptic seizure. The tonic

and clonic spasm is clearly visible after head-only

stunning. When a one-step head-to-body method

is used, the seizure may be masked. Often a very

weak tonic and clonic movement is still visible.

If electroimmobilization is used to keep the carcass

still after stunning, it must be turned off because it

will totally mask the tonic and clonic spasms.

2. The electric stunner should be equipped with a

meter so that amperage levels can be monitored.

3. Monitor stunner operations for electrode place-

ment and vocalization during electric stunner

placement. Appropriate plant monitoring pro-

grams for evaluating the effectiveness of electric

stunning should be implemented.

4. Wet pigs to ensure good electric contact. They

should be wet but not dripping with water. Large

amounts of water dripping off the animal may

cause the current to pass over the surface of the pig

instead of through the brain. For sheep, cattle, and

other animals with wool or hair, a small stream of

water should be applied either through the elec-

trode or right beside it to wet the application area.

5. Make sure animals are not dehydrated. Dehydrated

animals are more difﬁcult to render unconscious

with electricity.

6. Use a bleeding knife and techniques that will pro-

duce a stream of blood at least 2.5 cm wide in pigs.

A copious blood stream helps prevent problems

with return to consciousness.

119

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 39

7. When head-only stunning is used, equipment

should be designed so that the animals are bled

within 15 seconds after stunning. Well-designed

commercial plants that perform religious slaugh-

ter with head-only stunning have equipment that

is capable of achieving this goal. The two main

methods for achieving rapid bleeding are either

high-speed hoists or bleeding the animal on a table

immediately after it is ejected from the stun box or

restrainer.

8. The electrodes must be kept clean. A wire brush

should be used to clean the electrodes several times

each day.

9. Stunning tongs or wands should be ergonomically

designed to reduce operator fatigue.

10. Rotate the operators to help prevent fatigue. Data

collected from an electronically monitored stun-

ning unit showed that after 3 hours, the operator

was more likely to fail to ﬁrmly press the electrode

against the animal. Firm contact is essential for an

effective stun.

130

11. Both sides of a V conveyor restrainer should run

at the same speed. If one side runs faster than the

other, the animals will become agitated.

12. Use insulated restraint equipment. Plastic slats are

recommended on V conveyor restrainers, and there

should be no exposed bolts. When single-animal

restrainers are used, they should be insulated with

plastic meat cutting board.

13. For operator safety, all electric stunners should be

equipped with an isolation transformer or other

device that will prevent electricity from ﬂowing

from a single electrode to ground. The electricity

should only ﬂow between the two electrodes. The

metal frame of the restrainer and operator catwalk

must be connected to a good ground.

14. All electric components such as the stunner switch,

plugs, cords, and control box should be kept dry.

The only part of the stunner that should be wet-

ted is the electrodes. When the plant is cleaned,

the stunning tongs or wand should be removed and

stored in a dry location. The stunner control box

should be either placed in a separate dry room or

kept covered during plant wash down.

15. Several types of restrainers (for head and body)

can be employed for a variety of species. Cattle,

for example, must have a properly designed head

restraint. A head holding device is usually not re-

quired for pigs or sheep.

16. Employee training is essential.

t2.3 otHer pHysiCAl metHods

T2.3.1 Decapitation

Decapitation is not commonly employed in the

commercial slaughter of food animals, but is often used

for on-the-farm slaughter, primarily of poultry and rab-

bits.

137

When properly employed, this technique can be

a quick and humane method of slaughter, but if done

incorrectly, it has the potential to induce pain and dis-

tress on the animals. This method may be found to be

aesthetically displeasing to those performing or observ-

ing the technique.

In poultry killed by decapitation, convulsions fre-

quently occur immediately to several seconds follow-

ing application of the technique. Postmortem convul-

sions were minimized when chickens were electrically

stunned prior to decapitation.

143

Decapitation without prior stunning is rarely used

in poultry slaughter plants.

121

Decapitation is also a

method that is sometimes used for home slaughter of

poultry.

137

Early studies

144–146

on the effects of decapita-

tion on brain electric activity in chickens, sheep, and

rats showed persistence of activity for up to 13 to 14

seconds following decapitation, resulting in the conclu-

sion that the animals’ heads remained conscious dur-

ing this time and may have experienced pain. However,

many recent studies

147–150

have shown that this activity

does not imply the ability to perceive pain, and they

conclude that loss of consciousness occurs rapidly fol-

lowing decapitation. The concern that the blow from

the decapitating device might induce pain is mitigated

by the fact that afferent sensory nerves for the head and

neck enter the spinal cord at the level of the second cer-

vical vertebrae in most species; therefore, the severing

of the spinal cord at or above that level would prevent

sensory input from the tissue injury from reaching the

brain.

150

Operator competence is required to perform de-

capitation in a humane fashion. The operator must

be familiar with the technique and able to accurately

place the blade high on the neck, ideally at the level

of the ﬁrst vertebra. Blades used for decapitation must

be maintained to be kept sharp and able to sever the

entire head without need for more than one blow. Ani-

mals must be restrained to prevent them from moving

away from the blade. For poultry, restraint in a bleed-

ing cone will not only facilitate accurate aim, but will

also minimize tissue trauma from postmortem convul-

sions. Electrically stunning a bird prior to decapitation

reduces the occurrence of postmortem convulsions.

143

T2.3.2 Cervical dislocation

Cervical dislocation is not commonly employed in

the commercial slaughter of food animals, but is often

used for on-the-farm slaughter, primarily of poultry

and rabbits,

151

therefore the Panel has opted to provide

guidance.

For poultry, the legs of the bird should be grasped

(or wings if grasped at the base) and the neck stretched

by pulling on the head while applying a ventrodor-

sal rotational force to the skull. Crushing of cervical

vertebrae and spinal cord is not acceptable unless the

bird is ﬁrst rendered unconscious. Personnel should be

trained on anesthetized or dead animals to demonstrate

proﬁciency.

Data suggest that electrical activity in the brain

persists for 13 seconds following cervical dislocation

in rats,

148

and unlike decapitation, rapid exsanguina-

tion does not contribute to loss of consciousness.

149,150

For some classes of poultry, there is evidence that

cervical dislocation may not cause immediate

unconsciousness.

145,152–154

Cervical dislocation is a method that may induce

rapid loss of consciousness,

148,155

does not chemically

contaminate tissue, and can be rapidly accomplished.

However, cervical dislocation may be aesthetically

40 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

displeasing to personnel performing or observing the

method, and it requires mastering technical skills to en-

sure loss of consciousness is rapidly induced.

Manual cervical dislocation must be performed by

individuals with a demonstrated high degree of techni-

cal proﬁciency. In lieu of demonstrated technical com-

petency, animals must be unconscious or anesthetized

prior to cervical dislocation. When performed on poul-

try, cervical dislocation must result in luxation of the

cervical vertebrae without primary crushing of the ver-

tebrae and spinal cord. In some classes of poultry, there

is evidence that cervical dislocation may not cause im-

mediate unconsciousness.

145,152–154

In these cases, other

physical methods such as blunt force trauma or decapi-

tation may be more humane

156

and should be employed

when available or practicable.Those responsible for the

use of this method must ensure that personnel perform-

ing cervical dislocation have been properly trained and

consistently apply it humanely and effectively.

a. Meyer RE, Mississippi State University, Mississipi State, Miss:

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b. Vizzier-Thaxton Y, Professor and Director, Center for Food Ani-

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sonal communication, 2012.

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44 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

Animal and

method Head Tongue Back Eyes Limbs Vocalization Respiration Tail Response to pain

Cattle

Captive bolt Must appear dead, Straight and limp Hanging straight, No natural blinking. Wide open, Uncoordinated kicking of hind None Rhythmic breathing (ribs moving in and Relaxes shortly after being A pinch or pinprick may

hang straight and ﬂoppy no righting reﬂex blank stare, no response to touch; legs acceptable, no righting out at least twice) is absent. Agonal on the rail be applied to nose only

nystagmus absent reﬂex present gasping not acceptable. and no response should

be observed.

Electric Must appear dead, Straight and limp Hanging straight, Eyes may vibrate (nystagmus), but Uncoordinated kicking of hind None Agonal gasping like a ﬁsh out of water Relaxes shortly after being A pinch or pinprick may

hang straight and ﬂoppy no righting reﬂex no natural blinking legs acceptable, no righting normal. Rhythmic breathing (ribs moving on the rail be applied to nose only

reﬂex present in and out at least twice) is absent. and no response should

be observed.

Pigs

Must appear dead, Straight and limp Hanging straight, No natural blinking Uncoordinated kicking of hind None Agonal gasping like a ﬁsh out of water Relaxes shortly after being A pinch or pinprick may

hang straight and ﬂoppy no righting reﬂex legs acceptable, no righting normal. Rhythmic breathing (ribs moving on the rail be applied to nose only

reﬂex present in and out at least twice) is absent. and no response should

be observed.

Electric Must appear dead, Straight and limp Hanging straight, Eyes may vibrate (nystagmus), Uncoordinated kicking of hind None Agonal gasping like a ﬁsh out of water Relaxes shortly after being A pinch or pinprick may

hang straight and ﬂoppy no righting reﬂex but no natural blinking legs acceptable, no righting normal. Rhythmic breathing (ribs moving on the rail be applied to nose only

reﬂex present in and out at least twice) is absent. and no response should

be observed.

Captive bolt Must appear dead, Straight and limp Hanging straight, No natural blinking. Wide open, Uncoordinated kicking of hind

hang straight and ﬂoppy no righting reﬂex blank stare, no response to touch; legs acceptable, no righting None Rhythmic breathing (ribs moving in Relaxes shortly after being A pinch or pinprick may

nystagmus absent reﬂex present and out at least twice) is absent. Agonal on the rail be applied to nose only

gasping not acceptable. and no response should

be observed.

Sheep

Electric Must appear dead, neck Straight and limp Owing to Eyes may vibrate (nystagmus), Uncoordinated kicking of hind None Agonal gasping like a ﬁsh out of water Relaxes shortly after being A pinch or pinprick may

hangs on angle with anatomic but no natural blinking legs acceptable, no righting normal. Rhythmic breathing (ribs moving on the rail be applied to nose only

limp and ﬂoppy head differences in reﬂex present in and out at least twice) is absent. and no response should

sheep, back may be observed.

not hang

completely

straight; no

righting reﬂex

Appendix

Signs of a properly stunned animal by stunning method.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 45

Unique Species Issues

U1 Additional Considerations: Bovine

u1.1 bulls

Large bulls, water buffalos, or American bison

with very thick and heavy skulls create challenges for

stunning with captive bolt. Some plants have solved

this problem by electing to shoot all bulls twice or by

switching to the use of a large-caliber ﬁrearm. While

the latter option has been found to be effective, use of

a ﬁrearm within the conﬁnes of a packing plant cre-

ates serious safety concerns. The newer, more powerful

Jarvis pneumatic captive bolt gun has largely overcome

these problems, but because of its size and weight, it

must be properly mounted on a balance for effective

positioning over the proper anatomic site. This has

caused some to consider use of the poll position rather

than the frontal site. Studies indicate that the poll po-

sition can be effective if the appropriate captive bolt

gun is used and when the muzzle is directed so that the

discharged bolt will enter the brain.

However, use of

the poll position for penetrating captive bolt stunning

is prone to problems associated with operator error re-

sulting in misdirection of the bolt (eg, into the spinal

cord) and a failure to render animals unconscious ow-

ing to a shallow depth of concussion (ie, failure of the

bolt to sufﬁciently penetrate the skull).

u1.2 Cull CoWs

Culling is a management decision designed to re-

move animals with undesirable characteristics or poor

performance. For example, when choosing which

animals to cull, cattlemen consider pregnancy status,

performance of a cow’s previous calves, age and teeth

wear, udder health and teat conformation, structural

soundness of feet and legs, evidence of health problems

such as cancer eye, and the animal’s disposition. The

primary reasons dairy cows are marketed for slaughter

are failure to become pregnant, mastitis, and lameness.

From the packer’s standpoint, the most desirable (or

most proﬁtable) cull cows are those that leave herds for

failure to become pregnant, since these animals are usu-

ally in the best (fattest) body condition. Most of these

animals, along with culled bulls, enter packing plants

that process ground beef. Culling of cows needs to be

done proactively to ensure that culled cows are suitable

for transport to slaughter. This is important to ensure

that the well-being of the cows is not compromised and

is more likely to result in useable product. Cows should

be culled before they become weak and debilitated.

Successful stunning of cattle (ie, cow rendered in-

sensible between stunning and death by exsanguina-

tion) requires a penetrating captive bolt with sufﬁcient

bolt speed and power to penetrate the cow’s skull. It

also requires accurate placement of the captive bolt de-

vice over the intended site. When stunning procedures

are properly applied, the likelihood of a return to sensi-

bility is believed to be low. However, a Canadian study

designed to assess the likelihood of a return to sensibil-

ity following penetrating captive bolt stunning suggests

differently. Thirty-two cull dairy cows were assigned to

either group A (20 cows), which received penetrating

captive bolt stunning followed by pithing (within 10

minutes of stunning), or group B, which consisted of

12 animals that were stunned but not pithed. Research-

ers observed that none of the 20 animals in the captive

bolt plus pithing group (group A) regained conscious-

ness, whereas ﬁve of 12 (42%) animals in group B (ani-

mals that were not pithed) exhibited signs of a return

to sensibility (cattle that have been pithed are not con-

sidered acceptable or safe product for the human food

supply). Four animals were described as having clini-

cal signs consistent with reversible stunning, and one

demonstrated signs consistent with consciousness 20

minutes after being stunned with the captive bolt.

Be-

cause it is common practice to exsanguinate animals in

the packing plant environment, there may be less likeli-

hood that cows will return to consciousness. However,

these results do conﬁrm the need for an adjunctive step

whether the objective is slaughter or euthanasia.

Grandin

reports that the best packing plants are

able to achieve a successful ﬁrst shot stun on average

97% to 98% of the time. In an earlier study by Grandin

involving 21 packing plants, 17 successfully rendered

all cattle insensible before they were hoisted onto the

bleeding rail, whereas four plants had cattle showing

evidence of a return to sensibility that required restun-

ning. Of 692 bulls and cull cows, eight (1.2%) returned

to sensibility after stunning. Stunning failure was at-

tributed to storage of stunner cartridges in damp lo-

cations, poor cleaning and maintenance of the captive

bolt guns, dirty triggers that resulted in misﬁre of the

captive bolt, an inexperienced captive bolt operator

who shot cattle too high on the forehead, and stun-

ning of cattle with thick and heavy skulls.

A UK study

found that 1.7% of 628 cull cows were stunned poorly.

u1.3 nonAmbulAtory CAttle

On the basis of nonfed cattle reports

5–7

from feder-

ally inspected plants, the incidence of nonambulatory

animals during 1994 and 1999 was 1.1% to 1.5% for

dairy cows and 0.7% to 1.1% for beef cattle. During

2001, of 7,382 nonambulatory fed and nonfed cattle ar-

riving at 19 packing plants in Canada, 90% were dairy

cattle.

Furthermore, this study reported that < 1% of

the nonambulatory cases developed during the tran-

sit process. Nearly all developed the nonambulatory

condition on the farm of origin. A survey

of auction

markets where slaughter buyers purchase cull cows in-

dicated that 13.3% of the dairy cows and 3.9% of the

beef cows were severely emaciated. Severe emaciation

and weakness are factors that makes cows more likely

to become nonambulatory. There are a few medical rea-

sons why the downer cow condition is more common

in dairy cattle, but there is no good justiﬁcation for the

transportation of animals with a high probability of be-

coming recumbent. Producers must be vigilant in their

efforts to avoid transporting animals unﬁt for travel.

Cattle that are nonambulatory for a period of more

than 24 hours are commonly referred to as downers.

Occurrence is highest in dairy cattle and often traced

to metabolic disorders, injuries, and infectious or toxic

disease conditions. Periparturient hypocalcemia (milk

fever) and complications associated with calving are

the most common predisposing causes of the downer

cow condition. In fact, one study

identiﬁed the three

46 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

major causes of downer cow problems in dairy cattle

as hypocalcemia (19%), calving-related injuries (22%),

and injuries from slipping and falling (15%).

The pri-

mary cause of the downer cow syndrome in beef cattle

is calving paralysis.

Estimates are that about 5% of dairy cattle in the

United States have hypocalcemia annually. The major-

ity of cases (75%) occur within 24 hours of calving,

12% of cases within 24 to 48 hours of calving, and only

about 6% of cases at calving.

However, when hypocal-

cemia occurs prior to, or in association with, calving,

it can be an important contributor to dystocia and may

result in calving paralysis and associated complications.

Hypocalcemia is rare in beef cattle, but may occur in

conditions where severe dietary mineral imbalances are

present. The incidence of milk fever is low in sheep, but

may approach incidence rates similar to dairy cattle in

dairy goats with high milk yield.

Calving paralysis is a common cause of recumben-

cy in cattle. It is usually the consequence of attempts

to deliver a large calf relative to the pelvic size of the

cow. Paralysis results from damage to branches of the

ischiadic (sciatic) and obturator nerves, which are vul-

nerable to compression at calving by virtue of their po-

sition within the birth canal.

Traumatic injuries may be the primary cause of

recumbency, or they may occur as a secondary conse-

quence of a cow that is down and struggling to rise.

Examples of such lesions would include sacroiliac

(hip) luxation, coxofemoral luxation (uni- or bilateral),

pelvic or other fractures, and rupture of the gastroc-

nemius tendon. These injuries also occur as a conse-

quence of slips and falls. Injuries of the upper leg and

pelvis increased signiﬁcantly in cows during the sum-

mer months in a southeastern dairy as a result of wet

concrete ﬂooring conditions.

U1.3.1 Downer cow syndrome

Cows recumbent for prolonged periods are also

subject to peripheral nerve injury and muscle dam-

age that can increase the odds of a permanent nonam-

bulatory state. Because of its sheer size and weight, a

nonambulatory cow develops tremendous pressure on

tissues of the downed leg, leading to decreased blood

ﬂow, hypoxia, and pressure necrosis of muscle and pe-

ripheral nervous system tissues. Because of its anatomic

location, injury to distal branches of the sciatic nerve

is particularly common in recumbent cattle. Ischemic

damage to heavy muscles of the rear legs results in vary-

ing degrees of paresis that complicate the possibilities

of recovery in affected animals. The corollary to this

condition in humans is compartment syndrome.

The threshold for induction of permanent recum-

bency (down and unable to rise) in dairy cattle seems to

be as short as 6 hours. Of 84 periparturient cows down

with hypocalcemia, 83 (98.8%) recovered when treat-

ment was instituted within 6 hours after they became

recumbent.

Similarly, a survey

of dairy producers in-

dicated that nonambulatory cattle that recovered and

remained in the herd were down for < 6 hours. While

good footing, attitude of the cow, and body condition

are fundamental to care for nonambulatory animals, re-

search from a UK study

suggests that good nursing

care may have the single greatest effect on improving

the prognosis for nonambulatory cattle.

U1.3.2 The prevention of nonambulatory cattle

and downer cow syndrome

Many of the conditions that predispose to nonam-

bulatory cattle occur around the time of calving. As in-

dicated previously, the primary risk factors for recum-

bency are hypocalcemia, complications associated with

calving, and injuries. Close observation of cattle during

the transition period (4 weeks before and after calv-

ing) and particularly during the periparturient period

is essential to correct or treat problems promptly and

as necessary. Transition cow personnel should be well

trained and knowledgeable of transition cow problems.

Early detection and treatment of hypocalcemia (ie, be-

fore the cow goes down) will reduce the potential for

hypocalcemia-related complications. Cattlemen, dairy-

men, and dairy personnel who manage calving cows

need continual training and updates on proper ways to

assist cows with dystocia problems.

Finally, since many of the problems are related to

injuries from slipping and falling, it is important that

dairy operators be aware of ﬂooring conditions that

might predispose to falls. Some operations keep a log of

areas where slips and falls commonly occur. This infor-

mation can be used to determine when or whether cor-

rective action must be taken (eg, altering of the ﬂoor-

ing surface to increase traction). Owners and managers

should also ensure that personnel move animals with

care to avoid needless injury associated with careless

handling and cattle-driving procedures. No one should

assume that such information is common knowledge.

Good operations continually review their cattle-han-

dling procedures to avoid unnecessary injury to cattle

as well as personnel.

u1.4 bob VeAl

Calves ﬁtting the deﬁnition of bob veal are those

slaughtered within the ﬁrst few days of life. Most are

male calves from the dairy industry. These are to be dis-

tinguished from formula-fed (or milk-fed) veal, which

are older calves raised on a milk formula supplement.

Veal is one of the most controversial welfare issues

in modern agriculture. Those who oppose the raising

of veal generally cite tethering of formula-fed calves in

individual stalls that does not permit the calf freedom

to turn around as one of the major breaches of animal

welfare in veal production.

Neonatal calves require greater effort and care in

handling. Since they are removed from the dam at birth,

they tend to imprint on humans. They have little natu-

ral fear of humans and do not exhibit the ﬂight-or-ﬁght

responses normally observed in older calves. Moving

them requires actually picking them up or carefully

pointing them in the desired direction. They are in-

capable of responding to an electric prod, and use of

such devices becomes little more than torture. For busy

people unaccustomed to neonatal calf handling, the

process can be painfully slow and cumbersome.

Bob veal calves are typically transported from the

dairy to a packing plant or other gathering location

within 24 to 48 hours of birth. Transport to slaughter

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 47

may require as much as 12 to 24 hours; animals that

have not received an initial feeding of colostrum or

milk arrive at the plant with varying degrees of hypo-

glycemia and physical exhaustion. Some of these calves

will be nonambulatory on arrival at the plant. Under

its current rules, the FSIS will permit these animals to

be set apart and held for treatment before being moved

to slaughter. The Humane Society of the United States

petitioned the FSIS to amend the regulations to require

that nonambulatory disabled veal calves be condemned

and promptly and humanely euthanized. On April 4,

2011, the AVMA sided with the Humane Society of the

United States and recommended that this provision be

repealed to be consistent with the AVMA’s current pol-

icy on disabled livestock, which states the following:

If an animal is down at a terminal market (e.g., slaugh-

terhouse or packing plant)

Animals that are down should be euthanatized im-

mediately and not taken to slaughter. However, if swine

are down, and are not in extreme distress or do not

have an obviously irreversible condition, they may be

allowed up to 2 hours to recover. Acceptable interven-

tions to assist in this recovery include rest, cooling, or

other treatments that do not create drug residue con-

cerns.

On March 13, 2013, the FSIS decided to grant the

petition, resolving one of the more challenging prob-

lems for regulators and others concerned about ensur-

ing the welfare of nonambulatory calves at slaughter.

u1.5 fetAl effeCts

A 2002 report

suggested that world demand for

fetal calf serum was 500,000 L/y and growing, a need

that would require the harvest of at least 1,000,000

fetuses/y. To serve this need and safeguard fetal welfare,

it is important to understand what happens to the fetus

when its dam is slaughtered.

Behavioral and EEG evidence to date indicates

that mammalian fetuses are insentient and uncon-

scious throughout the ﬁrst 75% to 80% of gestation.

As neuronal pathways between the cerebral cortex and

thalamus become better established, the fetus develops

the capacity for sentience. However, within the pro-

tected environment of the uterus, the fetus remains in

an unconscious state due to the presence of eight or

more neuroinhibitors that act on the cerebral cortex

to maintain it in a sleep-like state of unconsciousness.

At birth, the combined effects of reduced neuroinhibi-

tion and onset of neuroactivation contribute to grad-

ual arousal of the mammalian newborn into a state of

consciousness.

These observations indicate that the fetus does not

suffer as if drowning in amniotic ﬂuid when the dam

is slaughtered, nor is it likely to experience conscious

pain associated with other types of invasive procedures

in utero. These studies also support the rationale for

international guidelines on the handling of fetuses sug-

gesting that fetuses should not be removed from the

uterus before the EEG is found to be isoelectric. For

example, when animals are killed by physical methods

that include exsanguination, delaying removal of the

fetus from the uterus for a minimum of 5 minutes after

hemorrhaging has ceased generally assures a substan-

tial amount of anoxia-induced damage to the cerebral

cortex that will normally prevent progression toward a

return to consciousness.

If there is any doubt as to the

fetus’s level of consciousness, it should be euthanized

immediately by captive bolt and adjunctive methods as

appropriate.

U2 Additional Considerations: Swine

u2.1 nonAmbulAtory sWine

Lameness disorders that interfere with locomotion

and contribute to nonambulatory conditions in pigs

include foot disorders (foot rot, overgrown claws, and

torn dewclaws), leg injuries, leg weakness (epiphysio-

lyis, apophysiolysis, osteochondritis, and arthrosis), os-

teomalacia, fractures, arthritis, and various neurologic

disorders. Although many of these conditions may not

result in nonambulatory conditions, all are signiﬁcant

causes of lameness that in their severest form, or when

complicated by other conditions, can lead to nonambu-

latory conditions.

Foot problems are reportedly one of the single most

important causes of lameness in sows.

21,22

Slatted con-

crete ﬂoors contribute to trauma of claws as feet slide

outward when the sow attempts to stand. Overgrowth

of claws, particularly on the lateral digits, is a serious

problem where sows are kept on nonabrasive ﬂoors

such as plastic or steel slats.

Foot rot and claw lesions

(erosions, white line disease abscesses, and vertical wall

cracks) are common disorders as well, with occurrence

rates as high as 64% in slaughter-weight pigs.

Results of several studies suggest that osteochon-

dritis (a degenerative disease of the articular or joint

cartilage) is the most common cause of lameness in

breeding-age animals. The joints mature by age rather

than weight. In rapidly growing animals, the excess

load on joints leads to disturbed development of the

joint cartilage on both the physeal and epiphyseal sur-

faces. This is followed by bony changes that form in

response to damage caused by mechanical stress and

load on the joints.

It is a major cause of leg weakness

in growing boars and sows.

Fractures are most often the result of falls on slip-

pery concrete or falls that may occur during transport.

They also result from situations where an animal’s foot

or leg becomes trapped beneath a feeder, in a slat, or

between pen rails. As the animal struggles to free it-

self, it fractures the limb. The lameness that results is

severe and often manifested by the carrying of the af-

fected limb. Failure to apply weight to a limb is a good

indication of a fracture. Fortunately, these are not com-

mon causes of lameness or nonambulatory conditions

in pigs.

In addition to these causes, there are neurologic

disorders affecting the spinal cord and brain. An early

study by Vaughan

suggests that the most common

cause of posterior paralysis in pigs of all ages is com-

pression of the spinal cord secondary to abscess forma-

tion of an intervertebral disk, vertebral body, or adja-

cent paravertebral tissues. Causes in adult animals are

believed to be associated with excess load on vertebral

disks that causes premature disk degeneration or osteo-

chondrosis of the vertebrae. In growing animals, spinal

abscesses are secondary to tail biting. These cases usu-

ally require euthanasia.

48 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

The incidence of transport losses in market-weight

pigs (dead and nonambulatory) is approximately 1%.

26,b

In a study

to evaluate the effect of ﬂoor space on trans-

port losses, Illinois researchers observed 74 loads of

ﬁnishing pigs; one load had 0.39 m

/pig and another

0.48 m

/pig during transport. Investigators monitored

the incidence of nonambulatory pigs at the farm dur-

ing loading and at the plant after unloading. Of 12,511

pigs transported, 32 (0.26%) were identiﬁed as non-

ambulatory on the truck at the farm, 29 (0.23%) were

dead on arrival at the plant, and 106 (0.85%) were non-

ambulatory at the plant. For 65 of 74 loads, pigs that

were nonambulatory at the plant were divided into two

groups: nonambulatory injured and nonambulatory

noninjured. The ratio of noninjured (0.55%) to injured

pigs (0.24%) was 2:1. Overall, the total number of pigs

lost in 74 loads was 135 (1.08%), which is comparable

to previous studies. Increasing ﬂoor space did not af-

fect the incidence of nonambulatory injured pigs at the

plant, but it did reduce the percentage of nonambula-

tory noninjured pigs and thus total losses at the plant.

U2.1.1 Preventing nonambulatory swine

Lameness disorders involving the foot and leg

are complicated. There is no one solution to correct-

ing or preventing these conditions. But, ﬂoors are a

major consideration in the prevention of foot and leg

problems. Pigs housed on slatted ﬂoors had an inju-

ry rate of 44% compared with 28% of pigs housed on

solid ﬂoors.

Concrete ﬂoors caused more foot and leg

problems than did softer earthen ﬂoors or deep straw-

bedded surfaces, and perforated ﬂoors contributed to

an increase in injuries.

In farrowing stalls, plastic and

steel slats caused more lameness than did solid ﬂoors.

Flooring surfaces should provide good footing to pre-

vent slips and falls; however, achieving the ideal bal-

ance between adequate traction and a slippery surface

is difﬁcult. When surfaces are too soft or nonabrasive

claw horn wear is reduced, then claws overgrow rap-

idly. Foot trimming is required in these conditions, or

the overgrowth will lead to claw deformities that also

create strain on tendons of the lower leg. On the other

hand, excessively abrasive ﬂooring surfaces accelerate

wear and may contribute to foot problems from exces-

sive wear of the sole.

Softer ﬂooring conditions are also believed to be

beneﬁcial for decreasing the incidence of osteochondri-

tis. Even more important to the prevention of leg weak-

ness caused by osteochondritis is to avoid overfeeding

of gilts during the growing period. In one study,

gilts

fed ad libitum were culled earlier and at a higher rate

as a consequence of leg weakness, compared with gilts

fed on a controlled feeding schedule. Research

also

demonstrates that pigs need exercise to increase mus-

cular strength and to develop proper agility on differing

ﬂooring systems.

Other factors that can contribute to causing down-

er pigs is the Halothane gene. Market pigs that were

carriers (heterozygotes) had 0.27% death losses and if

they were homozygous negative 0.05%.

Fortunately,

the Halothane gene has been bred out of many swine

herds. It is not now a major cause of losses in the Unit-

ed States.

High doses of the b-agonist ractopamine

may contribute to downers and make pigs more difﬁ-

cult to handle.

It may also cause hoof cracking.

Pigs

that have received little or no contact with people in

their pens on the farm prior to loading may be more

likely to pile up and be difﬁcult to move. Swine that

have had previous experiences with handlers will be

easier to move.

35–37

Producers should walk their pens

during ﬁnishing to get pigs acclimated to people walk-

ing through them. This will make handling and loading

easier.

Fatigued nonambulatory pigs may be reduced

because the pigs will be less likely to become agitated

during truck loading or during handling at the plant.

U3 Handling and Slaughter of Rabbits

u3.1 HAndling proCedures for rAbbits

In the United States, rabbits are not covered by the

HMSA, and federal inspection of rabbit meat is volun-

tary, although individual states may have rabbit-speciﬁc

inspection requirements.

There are few USDA-inspect-

ed plants in the United States that process rabbits, and

most of the available information on rabbit processing

comes from Europe, where commercial rabbit process-

ing is more common. For interstate commerce, rabbits

not voluntarily inspected at slaughter by the USDA are

under the regulatory oversight of the FDA.

Rabbits are prey animals that retain behavioral

patterns similar to their wild counterparts,

and the

harvesting, transport, and handling of rabbits prior

to slaughter are stressful.

A 2-fold increase in serum

cortisol was seen in rabbits after transport regardless of

whether they endured rough or careful handling during

loading, indicating that the entire process was stress-

ful.

Other biomarkers of stress in rabbits include el-

evations in serum glucose, serum triglycerides, serum

aspartate aminotransferase, alanine aminotransferase,

glutamyltransferase, lactate dehydrogenase, creatinine

kinase, and myocardial creatinine kinase, as well as

decreases in serum tetraiodothyronine.

Elevations of

these values have been reported in rabbits during trans-

port and lairage.

The preslaughter environment presents the com-

bined effects of many emotional and physical factors.

Multifactor (social and nonsocial) stressors involved in

the preslaughter process can affect rabbit welfare as well

as meat quality.

Social and nonsocial stress may occur

owing to changes of environment: for example, new or

unfamiliar habitat, separation of familiar companions,

presence of strangers or exposure to a strange group,

destabilization of an established hierarchy, aggressive

encounters, alarm vocalizations, social disturbances

and handling, disruption of the social group, changes

in social structure, separation or mixing with unfamil-

iar animals, food deprivation, and climatic conditions.

High stocking densities in crates should be avoided to

minimize distress and trauma due to intraspecies ag-

gression; the recommended minimum ﬂoor space for

12-week-old rabbits is 1,800 cm

Critical points during transport are waiting time at

the farm before loading, loading, ventilation and tem-

perature during transport, loading stops, unloading, du-

ration of lairage, and environmental conditions during

lairage.

Although some research

has suggested that

transport conditions are more important than the time

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 49

of the journey, other studies

have shown decreased

welfare and carcass quality in rabbits experiencing pro-

longed transport to slaughter. Ideal temperatures for

rabbit transport are between 50° and 68°F (10° and

20°C), and temperatures above 95°F (35°C) or humid-

ity below 55% are detrimental to rabbit welfare.

It is

important to remember that when transport crates are

stacked, rabbits located centrally in the stack may be

prone to hyperthermia and poor ventilation, while rab-

bits in crates on the periphery may be subject to hypo-

thermia.

Crates for transport and lairage should have

solid ﬂoors to prevent urine and feces transfer from

higher crates.

Multiﬂoor cage stands can adversely af-

fect welfare if rabbits are left in them for long periods

of time.

Providing adequate ventilation, preventing expo-

sure to extreme temperatures, providing food and wa-

ter for prolonged lairage, and avoiding long delays be-

tween loading and transport or arrival and stunning are

important factors in maintaining rabbit welfare in the

preslaughter period.

Extended lairage times should

be avoided, and water should be provided when delays

between arrival and slaughter are expected; this not

only is good for animal welfare but reduces live weight

and carcass losses.

Lairage areas should be protected

from the elements to minimize exposure to temperature

extremes.

Commercial processing of rabbits in the United

States is generally performed in plants designed to

process poultry.

Rabbits should be stunned prior to

shackling; shackling and hanging of conscious rab-

bits should be avoided. Shackling has been shown to

be painful and distressful to poultry,

49,50

and without

research to show differently, it must be assumed that

it is also painful and distressing to conscious rabbits.

Although one paper

on halal slaughter of rabbits sug-

gests that shackling of rabbits by one leg and simulta-

neously performing deep throat cuts did not result in

signs of rabbit distress, there are questions about those

authors’ methodology. The primary criterion used to

determine distress was the presence of vocalization in

the rabbits; however, the throat cuts severed the trache-

as of these rabbits, thereby making vocalization impos-

sible. The authors indicate that other potential signs of

distress and sensibility, such as movement of mouth or

eye reﬂexes, were not recorded.

Successful stunning is characterized by cessation of

respiration, excessive salivation, and increased motor

activity consisting in the (eg. immediate onset of tonic

spasm followed by weak to heavy clonic spasms).

52,53

Not all animals develop convulsive muscle activity, and

cessation of rhythmic breathing is considered a more

reliable indicator of a successful stun,

although some

consider lack of corneal reﬂex as the best measure of

insensibility in rabbits.

Maria et al

studied ﬁve methods of electrostun-

ning for commercial rabbits (n > 50) using variable

voltages and frequencies. Voltages < 19 V were not

recommended. The most common parameters used in

commercial facilities were 49 V, 5.6 milliseconds, and

189 Hz for 3 seconds. These parameters did not pro-

duce changes in muscle pH.

Anil et al

recommend a

minimum current of 140 mA by application of 100 V to

obtain adequate stunning. The European Food Safety

Authority

recommends that 400 mA be used in head-

only stunning devices. Impedance from rabbit fur can

result in a wide range of achieved currents, resulting

in variation in the effectiveness of the stun. Stunning

devices should employ an impedance- or resistance-

sensing device that will prevent discharge in the event

of insufﬁcient stunning current; this will minimize

the risk of inadequate and painful mis-stunning. The

stunned state lasts for at least 22 seconds, although in

adequately stunned rabbits, insensibility lasts for at

least 71 seconds.

Captive bolt apparatus designed for waterfowl can

be used on rabbits.

With penetrating captive bolts, the

best stunning results are obtained with a shot to the

parietal bone near the sagittal line but without hitting

bone sutures.

This is achieved by placing the captive

bolt slightly paramedian on the front as close to the ears

as possible (Figure 15). It is essential to stabilize the

head to prevent misses.

Following electric or captive bolt stunning, rabbits

are immediately shackled and exsanguinated. Rabbits

must be killed within 35 seconds of electric stunning or

they may recover consciousness.

In commercial rabbit

plants in Europe, exsanguination commences within 5

to 8 seconds following stunning, with many managers

allowing no more than an average of 15 seconds.

45,54

Bleeding time is reported to be 10 to 12 seconds

to 2

to 3 minutes.

Decapitation is not commonly employed in the

commercial slaughter of rabbits, but is sometimes used

for on-the-farm slaughter.

Operator competence is re-

quired to perform decapitation in a humane fashion.

The operator must be familiar with the technique and

Figure 15—Recommended placement for captive bolt slaughter

of rabbits.

50 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

able to accurately place the blade high on the neck, ide-

ally at the level of the ﬁrst vertebra. Blades used for de-

capitation must be maintained properly; they must be

sharp enough to sever the entire head without need for

more than one blow. Rabbits must be restrained to pre-

vent them from moving away from the blade.

Cervical dislocation is also used for on-the-farm

slaughter of rabbits.

When performed by well-trained

individuals on appropriate animals, the method ap-

pears to be humane. However, there are few scientiﬁc

studies available to conﬁrm this observation.

For immature rabbits, the head is held in one hand

and the hind limbs are held in the other. The animal is

stretched, and the neck is hyperextended and dorsally

twisted to separate the ﬁrst cervical vertebra from the

skull.

60,61

Data suggest that electric activity in the brain per-

sists for 13 seconds following cervical dislocation in

rats,

and unlike decapitation, rapid exsanguination

does not contribute to loss of consciousness.

63,64

Cervical dislocation is a method that may induce

rapid loss of consciousness,

62,65

does not chemically

contaminate tissue, and can be rapidly accomplished.

However, cervical dislocation may be aesthetically

displeasing to personnel performing or observing the

method, and it requires mastering technical skills to en-

sure loss of consciousness is rapidly induced.

Manual cervical dislocation must be performed by

individuals with a demonstrated high degree of techni-

cal proﬁciency. In lieu of demonstrated technical com-

petency, animals must be unconscious or anesthetized

prior to cervical dislocation. For rabbits, the large mus-

cle mass in the cervical region makes manual cervical

dislocation physically more difﬁcult.

Those responsible for the use of this method must

ensure that personnel performing cervical dislocation

have been properly trained and consistently apply it

humanely and effectively.

U4 Slaughter of Food Fish Intended

for Human Consumption

u4.1 generAl ConsiderAtions

In the United States, ﬁsh are not covered by the

HMSA. In addition, these Guidelines do not address

ﬁshing or wild-caught aquatic animals for recreational

purposes. Euthanasia and depopulation of ﬁsh can be

found in separate AVMA documents devoted to those

topics. Slaughter is used primarily to describe the hu-

mane killing of animals intended for human consump-

tion for food or other uses (eg, agricultural harvest

[catﬁsh, salmon, and tilapia] and commercial ﬁshing

[wild-caught salmon, grouper, and snapper]).

It was thought that ﬁnﬁsh, amphibians, reptiles,

and invertebrates lacked the anatomic structures neces-

sary to perceive pain as we understand it in birds and

mammals. However, recent evidence indicates ﬁnﬁsh

possess components of nociceptive processing systems

similar to those found in terrestrial vertebrates,

62–64,67–79

though debate continues on the basis of questions of

the impact of quantitative differences in numbers of

speciﬁc components such as unmyelinated C ﬁbers in

major nerve bundles. Studies indicating that ﬁnﬁsh re-

sponses to pain represent simple reﬂexes

have been

refuted by studies demonstrating forebrain and mid-

brain electric activity in response to stimulation that

differs with type of nociceptor stimulation.

81,82

While there is ongoing debate about ﬁnﬁshes’,

amphibians’, reptiles’, and invertebrate animals’ abil-

ity to feel pain or otherwise experience compromised

welfare, the AVMA’s POE assumed a conservative and

humane approach to the care of any creature is warrant-

ed, justiﬁable, and expected by society, and the POHS

will support that approach. Slaughter methods should

be employed that minimize the potential for distress or

pain in all animal taxa, and these methods should be

modiﬁed as new taxa-speciﬁc knowledge of their physi-

ology and anatomy is acquired.

u4.2 prepArAtion And enVironment

for food fisH slAugHter

This section will consider ﬁsh welfare implica-

tions during harvesting when ﬁsh are removed from

their growth or production habitat and are transported

to slaughter. If possible, withholding food for 12 to 24

hours prior to slaughter will reduce regurgitation, def-

ecation, and nitrogenous waste production. The envi-

ronment should be as quiet and nonstimulatory as pos-

sible, and light intensity should be reduced if possible,

but with adequate lighting for personnel.

Water quality should be similar to that of the en-

vironment from which the ﬁnﬁsh originated, or opti-

mized for that species and situation, for the duration of

killing. If of acceptable quality for ﬁnﬁsh health, water

in which they have been housed or captured should

be used. Water quality should be monitored includ-

ing parameters such as oxygen, pH, CO

, salinity, am-

monia, and temperature and optimized for the species

of ﬁsh in question. Any necessary changes should be

done gradually to allow the ﬁsh to adjust. Supplemen-

tal aeration and temperature control may be used when

necessary. The addition of salt (2 to 8 g/L) to the wa-

ter can also decrease stress in freshwater ﬁsh during

holding periods.

Handling and crowding, as well as

time out of water, should be minimized as much as

possible to control and minimize physiologic stress to

ﬁsh. In addition, nets and tanks should be designed to

minimize physical injuries by using smooth materials

and surfaces appropriately designed for use with ﬁsh

and by checking on a regular basis for holes, tears, or

other changes that would compromise the integrity of

the materials used.

u4.3 metHods of slAugHter for food fisH

Tissue residues from the use of drugs and other

chemicals make many slaughter methods unacceptable

unless they have been approved by the FDA for this

purpose and appropriate withdrawal periods are fol-

lowed. Use of any unapproved chemicals for euthanasia

prohibits entry of the ﬁnﬁsh into the food chain, either

by rendering, as ﬁsh meal, or by distribution for direct-

ly consumed product.

Carbon dioxide is a drug of low

regulatory priority

that avoids unacceptable residues,

but it is not an FDA-approved method for killing aquat-

ic animals used for food. Physical methods for killing

ﬁsh include manually applied blunt force trauma to the

head, decapitation, and pithing.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 51

The following methods, or a combination of the

following methods, can be applied for slaughter of food

ﬁsh, providing they are performed with proper equip-

ment, properly maintained, by trained personnel who

are regularly monitored for proﬁciency.

Carbon dioxide

Immersion in CO

-saturated water causes narco-

sis and loss of consciousness after several minutes.

72,86

This method is most often used as the ﬁrst step of a

two-step process with another method such as exsan-

guination. Some species may exhibit hyperactivity pri-

or to loss of consciousness.

87,88

Purity and concentra-

tion of CO

are important for effectiveness. Only CO

from a source that allows for careful regulation of con-

centration, such as from cylinders, is acceptable. Care

must be taken when using CO

to prevent exposure

to personnel (ie, slaughter must be conducted in well-

ventilated areas).

Captive bolt

(most commonly nonpenetrating; one step)

This is a method usually applied to large ﬁnﬁsh

species.

The nonpenetrating captive bolt gun has ei-

ther a wide mushroom-shaped head or a ﬂat head that

does not penetrate the brain. In general, regular non-

penetrating captive bolt guns only stun animals. Cor-

rect positioning is critical for effective stunning (Figure

16).

Gunshot

This technique is primarily used with large ﬁsh

such as tuna. When aimed correctly, the bullet enters

the brain to cause immediate damage and brain death,

resulting in it being both a stun and kill method. Op-

erators using this method should be trained in the

proper aiming required to ensure the correct location

of the bullet to the brain of the ﬁsh and to ensure hu-

man safety (refer to the section Techniques—Physical

Methods—Concussive—Gunshot for further safety in-

formation).

Pithing

This method is similar to spiking, coring, or ike-

jime. A spike is quickly inserted into the brain of the

ﬁsh to cause immediate brain death, resulting in it be-

ing both a stun and kill method. Pithing can be used

either as a one-step stun and kill method or as a second-

ary kill method. The technique of ikejime originated in

Japan with the insertion of the spike directly into the

hind portion of the brain of the ﬁsh. Spiking, or ike-

jime, will kill the ﬁsh instantly and prevent stress to the

ﬁsh. There are two main ikejime methods (Figure 16):

from the side of the head or through the gill cover. The

ﬁrst method is used for most medium-sized ﬁsh where

a sharp spike is driven into the brain from the right

side of the head. The position of spiking is diagonal and

about 2 cm behind the eye. Smaller ﬁsh can be spiked

through the gill opening with a sharp knife. This will

both spike and bleed the ﬁsh. The aim of both methods

is to destroy the hind brain of the ﬁsh, which is the part

of the brain controlling movement.

Operators using

this method should be trained in the proper location

and timing of the pithing process to ensure minimal

stress and rapid brain death for the ﬁsh.

Manually applied blunt force trauma

(cranial concussion) followed by secondary kill step

Manually applied blunt force trauma (a rapid, ac-

curately placed blow of sufﬁcient energy to the cranium

with an appropriate-sized club) can cause immediate

unconsciousness and potentially death, but should be

followed by a secondary kill step such as exsanguina-

tion (the cutting of the gill arches to bleed the ﬁsh) or

pithing (destruction of brain tissue). The ﬁnﬁsh’s size,

species, and anatomy and the characteristics of the

blow (including its accuracy, speed, and club mass) will

determine the efﬁcacy of manually applied blunt force

trauma. The location of the blow should be targeted at

the area where the brain is closest to the surface of the

head and where the skull is its thinnest

(Figure 17).

Figure 16—Pithing of ﬁsh (also spiking, coring, ikejime): A spike is

quickly inserted into the hindbrain of the ﬁsh and immediately fol-

lowed by physical disruption of brain tissue by rotary movement

of the spike. This causes immediate brain death.

Figure 17—Recommended placement for percussive stunning of

ﬁsh.

52 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

Operators of the manual percussive stunning method

should be trained in the proper location of the blow

to the head and should be given frequent breaks and

rotated often to avoid operator fatigue Automated sys-

tems require training for operators on a regular basis

and a preventative maintenance program to ensure the

proper functioning of the equipment.

Decapitation followed by secondary kill step

Rapid severance of the head and brain from the spi-

nal cord, followed by pithing of the brain, will cause

rapid death and unconsciousness. Decapitation alone is

not considered a humane approach, especially for spe-

cies that may be particularly tolerant of low O

concen-

trations. Pithing helps ensure rapid loss of brain func-

tion and death for those species.

Cervical transection using a knife or other sharp

instrument inserted caudal to the skull to sever

the spinal cord and cervical vertebrae, followed

by secondary kill step

The rationale for this approach is similar to that for

decapitation (destruction of connections between brain

and spinal cord) and pithing (destruction of brain tis-

sue), except that the head is still physically attached by

musculature to the body.

Electrocution

An electric current is passed through the water con-

taining the ﬁsh for slaughter. The voltage and amperage

conditions of the electric current should be sufﬁcient

not only to stun the ﬁsh, creating immediate uncon-

sciousness, but also to kill the ﬁsh (electrocution). Op-

erators using this method should be sufﬁciently trained

in the level of electric current appropriate to be used

for the species of ﬁsh in question as well as in safety

measures for themselves (Table 3).

Exsanguination as a secondary kill step

Gill arches are cut to cause bleeding of the ﬁsh and

ultimately death. Exanguination without prior stun-

ning should be avoided, as ﬁsh may struggle intensely

with vigorous head shakes and tail ﬂaps.

100

Rapid chilling (hypothermic shock;

one step or two step)

This method of killing is not appropriate for tem-

perate-, cool-, or cold-water tolerant ﬁnﬁsh or other

species that can survive at 4°C (39°F) and below, nor

is it currently acceptable for medium- to large-bodied

ﬁnﬁsh because of surface-to-volume considerations.

Fish display vigorous movement upon chilling; live-

chilling decreases plasma glucose when compared with

no chilling before slaughter. This decreased plasma glu-

cose was once thought to be due to decreased stress

101

;

however, more recent literature shows that this is likely

due to rapid depletion of energy stores as a result of

struggling during capture.

u4.4 ConClusions

Food ﬁsh slaughter techniques are very diverse,

and ﬁsh species vary in their response to different

methods

102

such as sensitivity to oxygen deprivation

103

or tolerance for low temperatures. Therefore, slaughter

techniques should be continually researched and deter-

mined speciﬁcally for the food ﬁsh species in question.

U5 Handling and Slaughter of Ratites

Ratites are ﬂightless birds that include the ostrich,

emu, and rhea. Currently, ostriches and emus are raised

in several countries for slaughter purposes. Slaughter

facilities for ratites include commercial plants speciﬁ-

cally designed for these birds, custom slaughter plants

that process a broad range of species, and plants pre-

viously utilized for a different species that have been

adapted for ratites (eg, a beef slaughter plant adapted

for ostrich).

Regardless of the slaughter facility used, care

should be taken to avoid standing in front ratites dur-

ing handling or catching. They can kick forward, and

a kick from a slaughter-weight bird can cause severe

injury from the last phalanx of the third toe, which is

pointed and carries a claw. It is advised to stay at the

side or toward the rear of the bird for handling purpos-

es. Toe trimming of the birds is a husbandry option, but

the third toe plays a primary role as a lever for balance,

exertion of traction forces, and directional impetus dur-

ing locomotion,

104

and trimming can negatively affect

their balance making the birds prone to slipping in wet

conditions.

105

When slaughter-stage ratites are worked with,

highly stressed and aggressive birds should be caught

ﬁrst to prevent agitation within the rest of the group.

Handlers can capture individual ostriches by using a

shepherd’s crook or by catching the beak in one hand

and pulling the bird’s head down and in the direction

the handler wishes the bird to move. Another option

for moving an individual bird is described in the Os-

trich Business Chamber’s Code of Conduct

106

A minimum of three handlers is needed to restrain

an adult bird to avoid injuries to both the ostrich and

handlers. A handler must be positioned at each side of

the ostrich holding the wings. One of these handlers

Species Waveform Frequency (Hz) Electric ﬁeld strength (V/cm) Electric current density (A/dm2) Duration (s)

Atlantic salmon

sine 50–80 0.25–0.5 Insufﬁcient data 10

Rainbow trout

sine 50 Insufﬁcient data 8.3 5

Carp

sine 50 25.7 0.73 5

African catﬁsh

sine 50 18.8 1.5 5

Sea bass

sine 50 1 5 1

Halibut

sine 50 1 Insufﬁcient data 10

Nile tilapia

sine 50 12.5 1 1

Eel (2 steps)

sine 50 13 0.7 1

sine 50 3.3 0.17 300

Table 3—Electrical parameters recommended for different species of ﬁsh.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 53

must be positioned between the wing and tail, taking

hold ﬁrmly of both the wing and the tail. One handler

should be employed at the head where he holds the

neck-head junction while immediately putting a blind-

fold or hood over the head of the ostrich. The handler

at the head must prevent injury to the soft beak as well

as interference with respiration. After hooding, ostrich-

es will be calm and the handler can move to the wing,

while the handler at the wing moves backwards to the

tail from where the ostrich can be steered.

A shepherd’s crook is typically not required for

emus, and they do not respond well to hooding un-

less they have been restrained prior to placement of the

hood.

107

Lifting the tail up and holding the head down

make it more difﬁcult for ratites to forward kick and

injure personnel.

For lairage, it is important that all pens be round,

hexagonal, or octagonal in shape. This prevents the

birds from crowding into the corners of the pens and

injuring one another. Additionally, side walls should

be 1.7 to 2.0 m high to prevent birds from seeing dis-

tractions outside the pen.

108

Walls should also be con-

structed to handle the force of birds running or push-

ing against them.

108

It should also be noted that while

ratites are ﬂightless birds, they can jump over low fenc-

es.

108

It is important to avoid startling the birds, as they

will attempt to ﬂee and will injure themselves and each

other.

108

Any unexpected behavior by personnel may

startle the birds and result in rapid evasive behavior.

Low light levels and minimal noise in lairage may help

birds remain quiet and calm.

108

It is best to avoid mix-

ing birds from different farms, as they can be become

aggressive toward one another. Water should always

be freely available to the birds during lairage. Grooved

cement ﬂoors can cause birds to slip, and metal grids

placed on top of cement can dissuade birds from set-

tling and lying down. A ﬂoor system that is suitable for

ratites is metal mesh (1- to 1.5-cm sided square holes)

raised above a concrete ﬂoor.

108

There are no universally agreed-upon stunning

methods for ratites. A large number of ostriches are

slaughtered annually in South Africa, and electric head-

only stunning performed with handheld tongs is the

most commonly used method. The recommended elec-

tric stunning parameters for ostriches in South Africa

are a current of 0.4 to 0.6 A at 90 to 110 V for a dura-

tion of 4 to 6 seconds.

106

Glatz recommends stunning

emus using 120 V at 1.2 A for 10 seconds and ostriches

using 120 V at 1.2 A for 15 seconds.

107

An electric stun-

ning current > 0.4 A at 50 Hz alternating current used

in head-only application prevented recovery in 90% of

ostriches when they were bled within 60 seconds.

109

The return of rhythmic breathing movements indicates

the ﬁrst stages of recovery in birds following an elec-

tric stun.

110

Effective stunning can be presumed when

epileptiform activity is seen (ie, rigidity with ﬂexed legs

[tonic phase] followed by kicking of varied intensity

[clonic phase]).

106

The CFIA Manual of Procedures

111

includes recommendations for electric stunning (Fig-

ure 18; Table 4).

Chapter 7 of the Food and Agriculture Organi-

zation of the United Nations Guidelines for Humane

Handling, Transport and Slaughter of Livestock

112

rec-

ommends 1.5 to 2 A and 90 V for 10 to 15 seconds for

electric stunning of ostriches.

During traditional stunning with handheld tongs,

birds are held in a restraining area by gentle pressure

applied from behind on the tail feathers. The restrain-

ing area is often a V-shaped structure high enough that

the stunning operator is not kicked. After (or during)

stunning, the bird is rocked backward and a leg clamp

is placed over the legs, immobilizing the birds and al-

lowing them to be shackled. The birds are then hoisted

onto a 3.4-m rail and conveyed to an exsanguination

area. Some commercial ratite slaughter plants now use

a new restraining and stunning mechanism that com-

pletely encompasses the bird in a padded clamp holder

that restrains the legs and body at strategic points. The

head of the bird is placed into a box where the electric

current is applied. While the bird is being electrically

stunned, the box rotates 180° so that toe clamps can be

applied without any danger to the stunning operators.

The box is then opened, and the bird is hoisted and

conveyed for exsanguination.

108

An air-powered captive needle pistol can also pro-

duce an effective stun in birds.

113,114

When a captive

needle pistol is used, the needles should be applied at

the intersection of two imaginary lines drawn from the

ear on one side of the head to the inner corner of the

eye on the other side.

113,114

In a report to the American

Ostrich Association, the Texas Agricultural Extension

Service noted the use of a Schermer captive bolt stun-

Figure 18—The tongs should be placed on both sides of the head

behind the eyes and just over the outer ear openings. “X” indi-

cates where the electrodes should be applied to each side of the

animal’s head.

Birds Amperage Volts Frequency Seconds

Ostriches, rheas, and 0.12–0.4 230–300 50–60 4–6

emus (not hooded)

Ostriches, rheas, and 0.4 230–300 50–60 4–6

emus (hooded)

Table 4—Canadian Food Inspection Agency recommended pa-

rameters for electrical stunning of ratites. (Adapted from CFIA.

Meat and poultry products: manual of procedures. Chapter 12,

annex A—species-speciﬁc guidelines—red meat species: ratites.

Available at: www.inspection.gc.ca/english/fssa/meavia/man/

ch12/annexa7e.shtml. Accessed Sep 13, 2012. Reprinted with

permission.)

54 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

ner for the birds.

115

The CFIA Manual of Procedures

111

pertaining to ratites recommends a captive bolt device

with a short bolt and the smallest charge appropriate

for poultry or rabbits applied to the top of the head at

the midpoint of an imaginary line between the outer

openings (Figure 19).

The Ostrich Business Chamber also ﬁnds captive

bolt stunning to be acceptable.

106

However, Chapter 7

of the Food and Agriculture Organization of the United

Nations Guidelines for Humane Handling, Transport

and Slaughter of Livestock states that a captive bolt gun

is not suitable for stunning ostriches, as “[t]heir brain

is small and lobulated, and the bolt does not produce

proper concussion.”

112

Birds should be bled immediately after stunning

(within 60 seconds

105

) with a complete ventral neck cut

that severs both carotid arteries and both jugular veins

or thoracic sticking. The CFIA recommends that the

birds are bled out via a complete ventral cut of the neck

(both carotid arteries) or a thoracic stick within 15 sec-

onds of stunning so that consciousness is not regained.

Anecdotally there is better and faster bleed out when

both the neck cut and thoracic stick are performed.

U6 Handling and Slaughter of Alligators

In the United States, alligators are not covered by

the HMSA and are classiﬁed as seafood for federal meat

inspection purposes.

116

A small fraction of alligators are

harvested from the wild, but the vast majority of alli-

gators entering the hide and meat markets are raised

on alligator farms, primarily in the Southern and Gulf

Coast states. Historically, alligators have been farmed

primarily for their valuable hides, although in recent

years the value of alligator meat has increased substan-

tially.

117,118

Most farmed alligators are slaughtered on

farm prior to either processing on-site or shipment to

processing facilities. This minimizes damage to hides

that might occur during mass shipment of live animals.

Reptiles represent a taxa with a diverse range of

anatomic and physiologic characteristics such that it

Figure 19—Arrow indicates the direction that the stunning device

should be pointed and the entry point at the top of the animal’s

head.

is often difﬁcult to ascertain that a reptile such as an

alligator is, in fact, dead. Although reptiles respond

to noxious stimuli and are presumed to feel pain, our

understanding of their nociception and response to

stimuli is incomplete. Nevertheless, there is increasing

taxa-speciﬁc evidence

of the efﬁcacy of analgesics to

minimize the impact of noxious stimuli on these spe-

cies. Consequently, slaughter techniques that result in

rapid loss of consciousness and minimize pain and dis-

tress

should be strived for, even where it is difﬁcult to

determine that these criteria have been met.

Handling of alligators prior to killing should fol-

low standard welfare guidelines and best practices for

alligator management to minimize stress to the alliga-

tors and to minimize the risk of injury to alligators and

human personnel.

119

Personnel should have appropri-

ate training on the humane handling of alligators, and

every effort should be made to avoid stress or overheat-

ing of the animals.

Alligators possess unique anatomic and physi-

ologic traits that can make the assurance of quick and

humane death difﬁcult. Reptiles have relatively high

tolerance for hypoxia compared with mammals, mak-

ing techniques that deprive the brain of oxygen (eg,

exsanguination, decapitation) less effective at inducing

rapid death

120

; some reptiles may remain conscious up

to an hour following decapitation. Studies of varying

physical methods of euthanasia of American alligators

indicated that penetrating captive bolt, nonpenetrating

captive bolt, and pithing reduced brain wave activity

to levels equivalent to or below those of anesthetized

alligators; these methods were considered to be appro-

priate methods for euthanasia.

In contrast, severance

of the spinal cord alone resulted in brain wave activ-

ity that did not signiﬁcantly differ from awake animals;

for this reason, spinal cord severance alone (as occurs

during decapitation) was considered an inappropriate

euthanasia technique for American alligators. Percus-

sive stunning by a blow to the head with a hard imple-

ment is unlikely to cause death because of the size and

thickness of the alligator skull in market-size animals

(> 3 ft in length). Cervical dislocation is not considered

an acceptable method in alligators owing to the resis-

tance of the reptilian brain to hypoxia and to the thick-

ness of neck muscles making vertebral dislocation very

difﬁcult.

120

Proper placement of captive bolts or gunshots is

imperative to ensuring a rapid and humane death in

alligators. The brain of the alligator is relatively small

and is located immediately behind orbits and extends

caudally between the supratemporal fossae. To ensure

destruction of brain tissue, the captive bolt or gun-

shot must be placed on the midline between the orbit

and the cranial aspect of the supratemporal fossae. Al-

though an approach from behind the skull plate aiming

forward through the occipital bone is sometimes used

in wild alligator harvests, this approach is likely to only

sever the spinal cord without destroying the brain and

is therefore not appropriate. Figure 20 illustrates the

appropriate sites for captive bolt or gunshot placement

and for spinal cord severance or decapitation.

For purposes of humane slaughter, the following

methods are considered acceptable provided that they

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 55

are performed with proper equipment that is proper-

ly maintained by trained personnel who are regularly

monitored for proﬁciency: 1) Penetrating or nonpen-

etrating captive bolt ﬁrearms targeting the brain of the

alligator. Care must be used to ensure proper placement

to ensure destruction of brain tissue. 2) Gunshot deliv-

ered to the brain may be used providing the legal and

safety concerns (eg, ricocheting bullet fragments) of us-

ing ﬁrearms are addressed. Care must be used to ensure

proper placement to ensure destruction of brain tissue.

3) Decapitation or spinal cord severance is acceptable

only if immediately followed by pithing to ensure de-

struction of brain tissue. The following killing methods

are considered unacceptable for slaughter of alligators:

cervical dislocation, exsanguination, hypothermia, hy-

perthermia, suffocation, and drowning.

a. Gregory N. Anatomical and physiological principles relevant to

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euthanasia methods in American alligators (Alligator mississip-

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cessed Oct 2013.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 59

Design of Facilities and Slaughter

Process for Religious Slaughter

R1 Handling Procedures at Slaughter Plants

for Hoofstock

r1.1–r1.5 steps 1 THrougH 5

Refer to the chapter Design of Facilities and Slaugh-

ter Process for information on arrival at the plant, un-

loading, receiving, lairage, and handling. The proce-

dures for these steps are the same regardless of whether

the animals will be slaughtered via conventional or re-

ligious methods.

r1.6 step 6—restrAint

There are various methods used to restrain and po-

sition the animal for religious slaughter. In the United

States, there is an exemption from the HMSA

for reli-

gious slaughter, and methods for restraining the ani-

mal for religious slaughter are outside the jurisdiction

of USDA FSIS regulations, although Congress has also

declared religious slaughter to be humane. The area

covered by the handling exemption has been called the

area of “intimate” restraint by the FSIS. When an ani-

mal is slaughtered in accordance with the ritual require-

ments of the Jewish faith or any other religious faith

that prescribes a method of slaughter whereby the ani-

mal suffers loss of consciousness by anemia of the brain

caused by the simultaneous and instantaneous sever-

ance of the carotid arteries with a sharp instrument,

the HMSA speciﬁcally declares such slaughter and han-

dling in connection with such slaughter to be humane.

However, all procedures outside this area, which many

meat inspectors call the “bubble,” are beyond the area

of intimate restraint and are subject to FSIS oversight

the same as conventional slaughter. Unloading animals

from transport vehicles, lairage, driving the animals to

the restraint point, and insuring that the animal is un-

conscious with no corneal reﬂex before invasive dress-

ing procedures begin are under FSIS jurisdiction, the

same as conventional slaughter.

R1.6.1 Detection of problems

From an animal welfare standpoint, there are three

issues that occur during religious slaughter, which

uses a neck cut to create unconsciousness. They are

as follows: 1) stress, 2) pain or discomfort caused by

how the animal is held and positioned for religious

slaughter, and 3) the throat cut itself. Because the

HMSA regulations exempt restraint of animals for re-

ligious slaughter from the regulations that apply to re-

straint for conventional slaughter, some small religious

slaughter plants use stressful methods of restraint such

as shackling and hoisting of live animals even though

more welfare-friendly restraint equipment is avail-

able. Research has clearly shown that upright restraint

is less stressful than shackling and hoisting for sheep

and calves.

In one study,

restraining cattle on their

backs for over a minute caused more vocalization and

a greater increase in cortisol than upright restraint in a

standing position for a shorter period of time. Another

study

showed that cattle vocalized less in an upright

restraint compared to rotating boxes. The OIE also rec-

ommends that stressful methods of restraint, such as

shackling and hoisting, shackling and dragging, and

leg-clamping boxes should not be used, and suspen-

sion of live cattle, sheep, goats, or other mammals by

their legs is not permitted in the United Kingdom,

Canada, Western Europe, and many other countries.

Fortunately most mid- to large-size religious slaugh-

ter plants in the United States have stopped this prac-

tice because of concerns for both animal welfare and

worker safety. One study

found that conversion of a

system that used shackling and hoisting to a conveyor

restrainer reduced worker injuries.

Upright restraint is less stressful for both mammals

and poultry, compared with being suspended upside

down.

2,6,7

Sheep were less willing to move through a sin-

gle-ﬁle chute after having been subjected to inverted re-

straint, compared with being put into a restraint device

in an upright position.

In two different plants where

cattle were suspended by one back leg, the percentage

of cattle that vocalized varied from 30% to 100%.

In-

creased percentages of cattle that vocalize (mooing or

bellowing) during restraint are associated with increased

cortisol levels.

In one study,

99% of the cattle vocaliza-

tions during handling and restraint were associated with

an obvious aversive event such as the use of electric

prods or excessive pressure from a restraint device. In

cattle, vocalization scoring is routinely used to monitor

handling and restraint stress,

10,11

and no more than 5%

vocalization (3% for nonreligious animal slaughter) is

acceptable according to the North American Meat Insti-

tute standards.

The difference in the percentages for ac-

ceptability relates to the differences in handling between

the two procedures. Vocalization scoring does not work

for evaluating the handling and restraint stress in sheep

because they usually do not vocalize in response to pain

or stress. This may be due to an instinctual inhibition of

vocalization in response to the presence of predators.

Research is needed to evaluate vocalization as a method

to evaluate stress in goats. The following methods of re-

straint are highly stressful for conscious mammals and

should not be used: hoisting and suspension by one or

more limbs, shackling by one or more limbs and drag-

ging, trip ﬂoor boxes that are designed to make animals

fall, and leg-clamping boxes. Even though suspension is

stressful for conscious poultry, such as chickens and tur-

keys, it is used in a vast majority of all US poultry plants

for both conventional and religious slaughter; with at-

tention to handling details and proper equipment, the

stress can at least be minimized.

R1.6.2 Corrective action for problems with restraint

For the religious slaughter of cattle, restraint de-

vices are available that hold the animal either in an up-

right position (Figure 21) or inverted onto their backs.

Smaller ruminants, such as sheep or goats, can be held

in an upright position by people or placed in a simple

restraint device.

Large heavy animals, such as cattle or

bison, must be held in a mechanical device that holds

them in an upright position, holds them in a sideways

position, or inverts them onto their backs. Vocaliza-

tion scoring of cattle can be used both to detect seri-

ous welfare problems during restraint of cattle and to

document improvements in either design or operation

of restraint devices. In cattle, when restraint devices for

60 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

religious slaughter are operated poorly or have design

problems, such as excessive pressure applied to the ani-

mal, 25% to 32% of the cattle vocalize.

9,13

In one study,

reducing pressure applied by a head-holding device re-

duced cattle vocalizations from 23% of the cattle to 0%.

These problems can occur in both upright and rotating

boxes. When the equipment is operated correctly, the

percentage of cattle that vocalize will be under 5%.

11,15,16

Inversion for over 90 seconds in a poorly designed ro-

tating box had a higher percentage of cattle vocalizing

and higher cortisol levels compared with holding in an

upright restraint box.

Information on the correct operation and design of

upright restraint devices for religious slaughter can be

found in reports by Grandin,

17,18

Grandin and Regen-

stein,

and Giger et al.

Upright restraint in a comfort-

able upright position is preferable. When a device that

inverts an animal is required by some religious leaders,

it should have adjustable sides that support the animal

and prevent its body from slipping, twisting, or falling

during inversion. Inversion onto the back facilitates

the downward cutting stroke. Upright or sideways (ly-

ing on the side) restraint may be less aversive than full

inversion. Hutson

found that full inversion was more

aversive to sheep than being held in an upright posi-

tion. Sheep can be easily trained to voluntarily enter a

tilt table, which tilts them sideways.

It is important to minimize the time that an ani-

mal is held ﬁrmly by a head restraint. Head restraint

using a mechanized device that tightly holds the head

is more aversive than body restraint.

Before the throat

cut, cattle that were held ﬁrmly in a head restraint often

struggle more than cattle held in a body restraint with

no head restraint.

Resistance to the head restraint oc-

curs after approximately 30 seconds; therefore, it is im-

portant to perform the throat cut before struggling or

vocalization begins. When struggling is being evaluated

from an animal welfare standpoint, only struggling that

occurs before loss of posture should be assessed. When

Velarde et al

evaluated struggling in different types

of restraint devices, they did not differentiate between

struggling before or after loss of consciousness. Strug-

gling while the animal is conscious is a welfare con-

cern, and struggling from convulsions after an animal

loses posture and becomes unconscious has no effect

on welfare. Restraint devices should be equipped with

pressure-limiting devices to prevent excessive pressure

from being applied, which then causes either struggling

or vocalization.

The percentage of cattle vocalizing

(mooing or bellowing) either while in a restraint de-

vice or while entering it should be 5% or less.

11,16

Re-

straint devices should not cause animals to struggle or

vocalize.

For poultry, stress during shackling can be

reduced by subdued lighting. Wing ﬂapping can be re-

duced by installing vertical pieces of conveyor belting

with a smooth surface for the breasts of the shackled

birds to rub on. A possible future method to reduce bird

stress while in shackles is the incorporation of a mov-

ing horizontal conveyor that supports the bird’s body.

A Dutch poultry plant recently installed a system where

each shackled chicken has its body supported in a plas-

tic holder.

In both large and small plants, where pos-

sible chickens can be held by a person in an upright

position for the throat cut and then placed immediately

either in a bleeding cone or on the shackle.

r1.7 step 7—performing tHe tHroAt Cut

There are three basic ways that religious slaugh-

ter is performed: 1) preslaughter stunning before the

throat cut with either a captive bolt or electric stun-

ning, 2) immediate postcut stunning with a nonpen-

etrating captive bolt, or 3) slaughter without stun-

ning (traditional hand slaughter). Some religious

Figure 21—Recommended restraint of cattle for religious or ritual

slaughter.

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 61

authorities who supervise either kosher (Jewish) or

halal (Muslim) religious slaughter will allow either

preslaughter or immediate postslaughter stunning.

For halal slaughter, electric head-only stunning is used

in many large cattle and sheep plants in New Zealand,

Australia, and the United Kingdom. Head-only elec-

tric stunning is acceptable to many Muslim religious

authorities because it is fully reversible and induces

temporary unconsciousness (refer to the section Tech-

niques—Physical Methods—Electric). If preslaugh-

ter stunning is done, there will be no animal welfare

concerns about the throat cut in a conscious animal.

Since most preslaughter stunning methods that are ap-

proved for religious slaughter produce a lighter revers-

ible stun, greater attention will be required to the de-

tails of procedures to ensure that the animals or birds

are and remain unconscious during the throat cut. An

effective reversible precut stun in sheep can be easily

achieved with 1.25 to 2 A at a frequency range of 50

to 400 Hz. According to Grandin,

when the stunner

was applied to the head for 1.5 seconds at 300 Hz, it

produced a clear tonic rigid phase followed by a clonic

kicking phase representative of an epileptic seizure.

This pattern is an indicator that it produced uncon-

sciousness. A modiﬁed New Zealand head-to-body

stunner with the rear body electrode removed worked

well because the design of the handle facilitated posi-

tioning of the stunner on the sheep’s head. In poultry

a very light reversible electric water-bath stun is done.

The preceeding stunning methods are acceptable to a

number of halal certiﬁers. Some halal certiﬁers will ac-

cept nonpenetrating captive bolt because the heart will

continue to beat after stunning.

Some religious com-

munities will accept immediate postcut stunning, and

others require slaughter without stunning (traditional

hand slaughter). Stunning methods are covered in the

Techniques chapter of these Guidelines.

R1.7.1 Detection of problems

The greatest welfare concerns may occur during

traditional religious hand slaughter. There are two main

issues: 1) Does cutting the throat of a conscious animal

cause pain? 2) What is the maximum appropriate time

that is required for the animal to become unconscious

after a properly done throat cut? The throat cut done

during both kosher and halal slaughter simultaneously

severs both carotid arteries and jugular veins and the

trachea. For halal slaughter, a sharp knife is required.

Kosher slaughter has more strict speciﬁcations for how

the cut is performed and the design and sharpening of

the knife.

28,29

A kosher slaughter knife is long enough to

span the full width of the neck (ie, double the width of

the neck) and is sharpened on a whetstone. Before and

after each animal is cut, the knife is checked for nicks

that could cause pain.

28,29

Any nick in the knife makes

the animal nonkosher, so there is a strong incentive to

keep the knife razor sharp and nick free.

R1.7.2 Painfulness of the cut

Researchers have reported that cutting the throat

of 107- to 109-kg (236- to 240-lb) veal calves with a

knife that was 24.5 cm long caused pain comparable

to dehorning.

30,31

The knife may have been too short

to fully span the throat, and it had been sharpened on

a mechanical grinder. A grinder may create nicks on

the blade and may not be comparable to a knife sharp-

ened on a whetstone. Slaughter without stunning of

cattle with a knife that is too short will result in vio-

lent struggling because the tip makes gouging cuts in

the wound.

One of the rules of kosher slaughter is

that the incision must remain open during the cut.

28,29

When the wound is allowed to close back over the

knife, cattle will violently struggle.

When an animal is

restrained in a comfortable upright position, it becomes

possible to observe how the animal reacts to the throat

cut. When a kosher knife was used by a skilled slaugh-

ter man (shochet), there was little behavioral reaction

in cattle during the cut.

18,19

In calves, there has been

a similar observation.

Grandin

reports that people

invading the animal’s ﬂight zone by getting near to the

animal’s face caused a bigger reaction. An eartag punch

has also caused a bigger reaction than a good kosher

cut.

Most chickens slaughtered by shechita exhibited

no physical response to the cut, and they lost the ability

to stand and eye reﬂexes at 12 to 15 seconds.

R1.7.3 Time to lose consciousness

Unconsciousness, as deﬁned in the General Intro-

duction of these Guidelines, is the loss of individual

awareness that occurs when the brain’s ability to in-

tegrate information is blocked or disrupted. Before

invasive dressing begins, all signs of brainstem func-

tion such as the corneal reﬂex must be abolished by

bleeding. Sheep will lose consciousness as determined

by their EEG more quickly than cattle because of dif-

ferences in the anatomy of the blood vessels that sup-

ply the brain.

34,35

In cattle, when the carotid arteries

are severed, the brain can still receive blood from the

vertebral arteries.

34,35

After the cut, sheep will become

unconscious and lose posture and no longer be able to

stand within 2 to 14 seconds, while most cattle will lose

consciousness and no longer be able to stand within 17

to 85 seconds.

36–42

In these studies,

36–42

time to onset of

unconsciousness was measured by either EEG or loss of

the ability to stand (LOP). Allowing the wound to close

up after a transverse halal throat cut with a 20-cm-long

knife may delay onset of unconsciousness. Electroen-

cephalographic measurements on sheep indicated con-

sciousness could last 60 seconds.

In a study

where

a rotating box was used to invert veal calves onto their

backs, unconsciousness was measured by EEG. It oc-

curred at an average of 80 seconds. In sheep, uncon-

sciousness as measured by time to eye rotation was 15

seconds.

There is a large amount of biological variability,

and a few cattle, calves, or sheep have extended peri-

ods of sensibility (> 4 minutes

42,46

). If the animals can

stand and walk they are deﬁnitely conscious. In sheep

the corneal reﬂexes, which are a brainstem reﬂex, may

be present for up to 65 seconds after the cut.

In veal

calves, corneal reﬂexes were still present at 135 ± 57

seconds after the throat cut.

The methods section

of Lambooij et al

did not describe the type of knife.

However, that study was done in a slaughter plant that

performed halal slaughter. Corneal reﬂexes can also

occur in electrically stunned or CO

-stunned animals

62 AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition

where other indicators of return to consciousness,

such as the righting reﬂex, rhythmic breathing, and eye

tracking, are absent.

Corneal reﬂexes occur during a

state of surgical anesthesia

or when visual potentials

and SEPs are abolished.

One of the best indicators for

determining onset of unconsciousness is the loss of the

ability to stand or walk (LOP). In cattle, a major cause

of prolonged periods of consciousness after the throat

cut is sealing off of the ends of the severed arteries (false

aneurysms).

This problem does not occur in sheep.

R1.7.4 Aspiration of blood

Another welfare concern is aspiration of blood into

the trachea and lungs after the cut.

In one study,

when cattle were held in a well-designed upright re-

straint, 36% (for kosher) and 69% (for halal) aspirated

blood. In 31% of these nonstunned cattle, blood had

been aspirated into the bronchi. It is likely that in a

rotating box where the animal is held on its back, aspi-

ration of blood will be higher.

R1.7.5 Corrective action for problems

To reduce painfulness of the act, a knife that is

long enough to span the neck where the tip will remain

outside the neck during the cut should be used.

It is

also essential that the knife be extremely sharp, and the

use of a whetstone is recommended. A good method

for testing a knife for sharpness is the paper test. To

perform this test, a single sheet of standard letter-size

(8.5 X 11-inch) printer paper is dangled in a vertical

position by being held by a thumb and foreﬁnger by

one corner. A dry knife held in the other hand should

be able to start cutting at the edge of the paper and slice

it in half. This method can eliminate the worst dull

knives, but it may not detect sharp knives with nicks.

It is also essential to not allow the wound to close

back over the knife during the cut. To prevent sealing

off of the arteries in cattle, the cut should be angled so it

is close to the ﬁrst cervical vertebra (C1) position

46,53

long as such a cut is accepted by the religious authorities.

This will also cut a sensory nerve, which may prevent

the cattle from experiencing distressful sensations from

aspirating blood.

46,53

The cut should be located posterior

to the larynx and angled toward the C1 position.

Before invasive dressing procedures such as skin-

ning or leg removal are started, the corneal reﬂexes must

be absent. Even though an animal showing only a cor-

neal reﬂex is unconsciousness, to provide a good margin

of safety, it should be absent before dressing procedures

start. Absence of the corneal reﬂex and complete un-

consciousness before dressing procedures are started are

best practices for all slaughter plants that conduct both

conventional slaughter and religious slaughter.

R2 Auditing Religious Slaughter to Improve

Animal Welfare for Both Kosher and

Halal Slaughter of Cattle, Sheep, or Goats

The following audit methods are recommended to

maintain an acceptable level of animal welfare when re-

ligious slaughter is performed by cutting of the neck.

1. Calm animals will lose sensibility quicker. Follow

all procedures for handling that are in other parts

of this document.

17,18

2. Conduct collapse-time scoring. When the best

methods are employed, 90% of the cattle will

collapse and lose the ability to stand within 30

seconds.

Researchers in Europe reported a simi-

lar result when they used a well-designed upright

restraint device.

In a rotating box, collapse-time

scoring is impossible because the animal is on its

back. Alternative measures for determining onset

of unconsciousness are time until eye rotation and

the amount of time to abolish the presence of natu-

ral blinking such as seen with a live animal in the

yards (lairage). Natural blinking must not be con-

fused with the corneal reﬂex. To evaluate natural

blinking (menace reﬂex), a hand is waved within

4 inches (10 cm) of the eye without touching it. A

natural blink occurs if the eye does a full cycle of

closing and then reopening. Omit scoring of time

to unconsciousness if pre- or postcut stunning is

used.

3. The vocalization score should be 5% or less for

cattle.

10,11

Score on a per-animal basis, as a silent

animal or a vocalizer (mooing or bellowing). All

cattle that vocalize inside the restraint device are

scored. A bovine is also scored as a vocalizer if it

vocalizes in direct response to being moved by a

person, electric prod, or mechanical device into

the restraint device. Do not use vocalization scor-

ing for sheep. Standards for vocalization scoring of

goats will need to be developed.

4. In all species, score restraint methods for the per-

centage of animals that actively struggle before LOP.

5. The percentage of animals (all species) that fall

down in the chute (race) leading up to the restraint

device or fall before the throat cut in the restraint

device should be 1% with a goal of zero. This is the

same as conventional slaughter. Restraint devices

that are designed to make an animal fall are unac-

ceptable and result in an automatic audit failure.

Rotating boxes must fully support the body, and

the animal’s body should not shift position or fall

when the box is rotated.

6. Electric prods should be used judiciously and only

in extreme circumstances when all other tech-

niques have failed.

Score prod use using the same

criteria as conventional slaughter.

7. Perform the cut quickly, preferably within 10 sec-

onds after the head is fully restrained. Omit this

measure if preslaughter stunning is used.

8. Reduce the pressure applied by the head holders

(but do not remove it), rear pusher gates, and other

devices immediately after the cut to promote rapid

bleed out.

9. Corneal reﬂexes, rhythmic breathing, and all other

signs of return to sensibility must be absent before

invasive dressing procedures such as skinning, leg

removal, or dehorning are started. This is a require-

ment for all methods of slaughter both conven-

tional and religious to be absolutely sure that the

animal is completely insensible.

10. Do not use stressful methods of restraint for mam-

mals, such as shackling and hoisting by suspension

by one or more limbs, shackling and dragging by

one or more limbs, trip ﬂoor boxes that are de-

AVMA Guidelines for the Humane Slaughter of Animals: 2016 Edition 63

signed to make animals fall, leg-clamping boxes, or

other similar devices.

11. If either pre- or postcut stunning is used, score the

same as conventional slaughter.

R3 Auditing Religious Slaughter to Improve Animal

Welfare for Both Kosher and Halal Slaughter

of Chickens, Turkeys, and Other Poultry

1. If stunning is used, audit and monitor the percent-

age of birds that are effectively stunned using the

same criteria as for conventional slaughter.

2. Score the performance of shacklers for faults such

as one-legged shackling using the same criteria as

for conventional slaughter.

3. There should be 0% uncut red skinned birds that

emerge from the defeathering machine. This is

an indicator that a bird entered the scalder alive.

This measure is the same as used for conventional

slaughter.

4. Score the percentage of birds that wing ﬂap af-

ter restraint. In a well-designed shackle line with

a breast rub conveyor, the percentage of ﬂapping

birds should be very low.

R4 The Importance of Measurement

By routinely measuring the performance of re-

ligious slaughter procedures, the standards for such

slaughter are kept high. Measuring collapse times for

unconsciousness or other indicators such as time to eye

roll-back or the absence of natural blinking will enable

both plant personnel and religious slaughter personnel

to improve their procedures.

a. Grandin T, College of Agricultural Sciences, Colorado State

University, Ft Collins, Colo: Personal communication, 2012.

b. Grandin T, College of Agricultural Sciences, Colorado State

University, Ft Collins, Colo: Personal communication, 2015.

c. Voogd E, Department of Animal Sciences, College of Agricultur-

al, Consumer and Environmental Sciences, Urbana, Ill: Personal

communication, 2009

R5 References

1. Humane Methods of Livestock Slaughter Act, 1958. CP.L. 85–

765; 7 U.S.C. 1901 et seg.

2. Westervelt RG, Kinsman DM, Prince RP, et al. Physiological

stress measurement during slaughter in calves and lambs. J

Anim Sci 1976;42:831–837.

3. Dunn CS. Stress reactions of cattle undergoing ritual slaughter

using two methods of restraint. Vet Rec 1990;126:522–525.

4. Verlarde A, Rodriquez P, Calmue A et al. Religious slaughter

evaluation of current practices in selected countries. Meat Sci

2014;96:278–287.

5. Grandin T. Double rail restrainer conveyor for livestock han-

dling. J Agric Eng Res 1988;41:327–338.

6. Bedanova I, Vostarova E, Chioupek P, et al. Stress in broilers

resulting from shackling. Poult Sci 2007;86:1065–1069.

7. KannAn G, Heath JL, Wabeck CJ, et al. Shackling of broilers:

effects on stress responses and breast meat quality. Br Poult Sci

1997;38:323–332.

8. Hutson GD. The inﬂuence of barley feed rewards on sheep

movement through a handling system. Appl Anim Behav Sci

1985;14:263–273.

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