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Euthanasia of Animals

By

Cia L. Johnson

, DVM, MS, MSc, American Veterinary Medical Association;


Emily G. Patterson-Kane

, PhD, American Veterinary Medical Association

Last full review/revision Feb 2020 | Content last modified Mar 2020

Euthanasia is the term used to describe a method of killing that minimizes pain, distress, and anxiety experienced by the animal before loss of consciousness. Techniques used in contexts such as pest control, slaughter, or depopulation may not always meet the criteria of euthanasia due to situational constraints.

Acceptable Techniques for Euthanasia of Animals

Animal slaughter, depopulation, and humane killing are distinguished from euthanasia, because they are performed for reasons different than sparing an animal from unresolvable painful or distressful conditions. Euthanasia of animals is a common procedure performed by veterinary professionals, and because of the seriousness of the action, it deserves appropriate consideration. Some of the most difficult euthanasia decisions that veterinarians are required to make involve the euthanasia of healthy animals when no other alternative for their care can be identified. A veterinarian must be fully prepared to speak frankly about the animal’s condition and be knowledgeable about all possible alternative care resources when interacting with animal owners, caretakers, and control professionals.

Recognizing the importance of a "good death" in the humane termination of an animal’s life, many countries and professional organizations have developed guidelines and recommendations for animal euthanasia; some are more specific for certain species and environmental settings. Most recommendations emphasize certain factors that personnel performing euthanasia should consider when selecting the best method to use:

  • ability of the method to induce loss of consciousness and death with minimal pain and distress

  • time required to induce loss of consciousness

  • reliability

  • safety of personnel

  • irreversibility

  • compatibility with intended animal use and purpose

  • documented emotional effect on observers or operators

  • compatibility with subsequent evaluation, examination, or use of tissue

  • drug availability and human abuse potential

  • compatibility with species, age, and health status

  • ability to maintain equipment in proper working order

  • safety for predators or scavengers should the animal’s remains be consumed

  • legal requirements

  • environmental impacts of the method or disposition of the animal’s remains

Euthanizing agents cause death by three basic mechanisms: 1) direct depression of neurons necessary for life function, 2) hypoxia, and 3) physical disruption of brain activity. Because loss of consciousness resulting from these mechanisms can occur at different rates, the suitability of a particular agent or method will depend on whether an animal experiences distress before loss of consciousness. Unconsciousness, defined as loss of individual awareness, occurs when the brain’s ability to integrate information is blocked or disrupted.

Table
icon

Agents and Methods of Euthanasia by Species

Species

Acceptable Methodsa

Acceptable Methods with Conditionsb

Aquatic invertebrates

S6.3c: Immersion in anesthetic solution (magnesium salts, clove oil, eugenol, ethanol)

S6.3: Adjunctive methods (second step) include 70% alcohol and neutral-buffered 10% formalin, pithing, freezing, boiling

Amphibians

S7.3: As appropriate by species—injected barbiturates, dissociative agents, and anesthetics as specified, topical buffered tricaine methanesulfonate or benzocaine hydrochloride

S7.3: As appropriate by species—inhaled anesthetics as specified, CO2, penetrating captive bolt or firearm, manually applied blunt force trauma to the head, rapid freezing of small (<4 g [0.1 oz]) individuals where immediate death occurs

Avian species (see also Poultry, below)

S5: IV barbiturates

S5: Inhaled anesthetics, CO2, CO, N2, Ar, cervical dislocation (small birds and poultry), decapitation (small birds)

S7.5: Gunshot (free-ranging birds)

Cats

S1: IV barbiturates, injected anesthetic overdose, Tributame, T61

S1: Barbiturates (alternative routes of administration), inhaled anesthetic overdose, COc, CO2c, gunshotc

Cattle

S3.2: IV barbiturates

S3.2: Gunshot, penetrating captive bolt

Dogs

S1: IV barbiturates, injected anesthetic overdose, Tributame, T61

S1: Barbiturates (alternative routes of administration), inhaled anesthetic overdose, COc, CO2c, gunshotc

Fish

S6.2: Immersion in buffered benzocaine or benzocaine hydrochloride, isoflurane, sevoflurane,quinaldine sulfate, buffered tricaine methanesulfonate, 2-phenoxyethanol, injected pentobarbital, rapid chilling (appropriate species), ethanol

S6.2: Eugenol, isoeugenol, clove oil, CO2-saturated water (aquarium-fish facilities/fisheries), decapitation/cervical transection/manually applied blunt force trauma followed by pithing or exsanguination, maceration (research setting), captive bolt (large fish)

Equids

S4: IV barbiturates

S 4: Penetrating captive bolt, gunshot

Marine mammals

S7.5(captive): Injected barbiturates (captive)

S7.7 (free-ranging): Injected barbiturates or anesthetic overdose

S7.5 (captive): Inhaled anesthetics (captive)

S7.7 (free-ranging): Gunshot, manually applied blunt force trauma, implosive decerebration

Nonhuman primates

S2.3, S7.4: Injected barbiturates or anesthetic overdose

S2.3, S7.4 (as appropriate by species): Inhaled anesthetic, CO, CO2

Poultry

S3.4: Injected barbiturates and anesthetic overdose

S3.4: CO2, CO, N2, Ar, low-atmospheric-pressure stunning, cervical dislocation (as anatomically appropriate), decapitation, manual blunt force trauma, electrocution, gunshot, captive bolt

Rabbits

S2.4: IV barbiturates

S2.4: Inhaled anesthetic overdose, CO2, cervical dislocation (as anatomically appropriate), penetrating captive bolt, nonpenetrating captive bolt

Reptiles

S7.3: As appropriate by species—injected barbiturates/buffered tricaine methanesulfonate, dissociative agents with adjunctive method and anesthetics as specified

S7.3: As appropriate by species—inhaled anesthetics as specified, CO2, penetrating captive bolt or firearm, manually applied blunt force trauma to the head, rapid freezing for animals <4 g where immediate death occurs, spinal cord severance/destruction of brain (crocodilians)

Rodents

S2.2: Injected barbiturates and barbiturate combinations, dissociative agent combinations

S2.2: Inhaled anesthetics, CO2, CO, tribromoethanol, ethanol, cervical dislocation, decapitation, focused beam microwave irradiation

Small ruminants

S3.2: Injected barbiturates

S3.2: CO2 (goat kids), gunshot, penetrating captive bolt, nonpenetrating captive bolt (goat kids)

Swine

S3.3: Injected barbiturates

S3.3: CO2, CO, N2, Ar, gunshot, electrocution, penetrating captive bold, nonpenetrating captive bolt (piglets), manually applied blunt force trauma

Reprinted, with permission, from the AVMA Guidelines on Euthanasia 2020 Edition. Note: Initial “S” references with associated numbers in table entries refer to specific areas of more detailed information in the AVMA guidelines, available at www.avma.org/sites/default/files/2020-02/Guidelines-on-Euthanasia-2020.pdf.

a Acceptable methods are those that consistently produce a humane death when used as the sole means of euthanasia.

b Acceptable methods with conditions are those that may require certain conditions to be met to consistently produce humane death, may have a greater potential for operator error or safety hazards, are not well documented in the scientific literature, or may require a secondary method to ensure death.

c Not recommended for routine use.

Ideally, euthanasia techniques cause rapid loss of consciousness, followed by cardiac or respiratory arrest and death. This may occur very rapidly in a technique, such as gunshot targeting the brain, or more gradually, with a method that first induces unconsciousness, such as anesthetic overdose. If loss of motor or respiratory and cardiac function precedes loss of consciousness, as might be the case if paralytic agents are used, animals may become fearful and experience distress, which is not acceptable.

For a list of acceptable methods and agents for euthanasia of different species of animals, see the accompanying table . The full AVMA Guidelines for Euthanasia 2020 provide information necessary to correctly select and implement these techniques.

The Context for Euthanasia of Animals

In most cases, the euthanasia of an animal occurs in a context with:

  • prior communication and decision making

  • planning for the euthanasia

  • staging and conducting the euthanasia

  • disposition of the remains

The emotional attachment between animals and their owners or caretakers requires an additional layer of professional respect and care. Discussing euthanasia openly allows everyone the opportunity to understand that the best interests of the animal, owners, and caretakers have been considered.

Veterinary professionals may have unfavorable experiences concerning the end of life resulting from conflict with clients, moral stress relating to participation and outcomes, internalizing the client’s grief, negative input from others, and lack of mental health support. Important mitigating factors are: 1) supportive practice policies with compassionate leadership, and 2) training in communication and deliberative frameworks. Early intervention for personnel experiencing unresolved stress or mental health problems is imperative. (See also Self-care for Veterinarians).

It is important that euthanasia is provided in a manner that minimizes distress to the animal and considers their natural behavior. A euthanasia approach that can be applied in familiar surroundings may help reduce distress. For animals accustomed to human contact, gentle restraint (preferably in a familiar and safe environment), careful handling, and talking during euthanasia often have a calming effect and may also be effective coping strategies for personnel and animal owners. Sedation and/or anesthesia may help to achieve the best conditions for euthanasia. It must be recognized that sedatives or anesthetics given at this stage that change circulation may delay the onset of the euthanasia agent.

Death must be confirmed before disposal of any animal remains. A combination of criteria is most reliable in confirming death, including:

  • lack of pulse, breathing, corneal reflexes and response to firm toe pinch

  • inability to hear respiratory sounds and heartbeat by use of a stethoscope

  • graying of the mucous membranes

  • rigor mortis

None of these signs alone, except rigor mortis, confirms death. Confirming death may best be accomplished by an adjunctive method (eg, thoracotomy, decapitation) performed after the loss of consciousness. Using an adjunctive method may be especially important when euthanizing ectothermic animals, because their heartbeat and respiration are difficult to assess. Animal remains must be disposed of in a legal manner that does not contaminate food sources or the environment.

Key Points

  • The euthanasia process should minimize or eliminate pain, anxiety, and distress before loss of consciousness.

  • Acceptable euthanasia techniques vary by species, age, and health status of the individual animal.

  • Euthanasia can be distressing for owners and veterinary professionals. This should be managed through open dialogue, compassion, and availability of mental health resources.

  • Death must be confirmed before disposal of any animal remains.

  • Animal remains must be disposed of in a legal manner that does not contaminate food sources or the environment.

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