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Find information on animal health topics, written for the veterinary professional.

* This is the Veterinary Version. *

Overview of Euthanasia

By Samuel C. Cartner, DVM, PhD, DACLAM, Assistant Vice President for Animal Research Services and Director, Animal Resources Program, University of Alabama at Birmingham

Euthanasia is the term used to describe ending the life of an animal in a way that eliminates or minimizes pain and distress. 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 of euthanasia. These factors include: 1) ability of the method to induce loss of consciousness and death with minimal pain and distress; 2) time required to induce loss of consciousness; 3) reliability; 4) safety of personnel; 5) irreversibility; 6) compatibility with intended animal use and purpose; 7) documented emotional effect on observers or operators; 8) compatibility with subsequent evaluation, examination, or use of tissue; 9) drug availability and human abuse potential; 10) compatibility with species, age, and health status; 11) ability to maintain equipment in proper working order; 12) safety for predators or scavengers should the animal’s remains be consumed; 13) legal requirements; and (14) environmental impacts of the method or disposition of the animal’s remains.

To be able to understand and help others to understand euthanasia, personnel performing euthanasia should be well informed of established definitions of the more important physiologic and psychological states that may be observed during euthanasia. The American Veterinary Medical Association Panel on Euthanasia accepts the following important definitions: 1) anesthetic-induced unconsciousness is the loss of the righting reflex; 2) pain is a conscious experience; 3) distress is an animal’s response to stimuli that interferes with its well-being and comfort. Thus, biological functions (urination, defecation), unintentional movements (limb paddling), and vocalizations after administration of an appropriate euthanasia method, and subsequent recumbency are not necessarily signs of perceived pain or distress. Loss of physiologic function and death should occur in the following order to help prevent fear and distress: 1) rapid loss of consciousness, 2) loss of motor function, 3) arrest of respiratory and cardiac functions, and finally 4) permanent loss of brain function. 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. In some species, particularly rabbits and chickens, tonic immobility may be induced by fear, and care must be taken to not confuse this behavioral response with loss of consciousness.

In addition to the selection of the method of euthanasia, the euthanasia administrator should consider the natural behavior of the species. For virtually all species, being placed in a novel environment before euthanasia is stressful. Therefore, a euthanasia approach that can be applied in familiar surroundings may help reduce distress. Gentle restraint, careful handling, and talking during euthanasia often have a calming effect on animals accustomed to human contact. These techniques may also be effective coping strategies with personnel and owners. In some species, sedation may assist in achieving the best conditions. The emotional attachment between animals and their owners or caretakers requires an additional layer of professional respect and care. Discussing euthanasia openly with personnel allows everyone the opportunity to understand that the best interests of the animal, owners, and caretakers have been considered.

Regardless of the method of euthanasia selected, personnel performing euthanasia must confirm death and dispose of the carcass in a legal manner that does not contaminate food sources or the environment. Confirming death may best be accomplished by an adjunctive method (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.

For a list of acceptable methods and agents for euthanasia of different species of animals, see Table: Agents and Methods of Euthanasia by Species. The AVMA Guidelines for Euthanasia 2013 (view the guidelines) provide additional details, as well as references for specific technical and safety information.

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

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

S1: Barbiturates (alternative routes of administration), inhaled anesthetic overdose, embutramide, T-61, COc, CO2c, gunshotc

Cattle

S3.2: IV barbiturates

S3.2: Gunshot, penetrating captive bolt

Dogs

S1: IV barbiturates, injected anesthetic overdose

S1: Barbiturates (alternative routes of administration), inhaled anesthetic overdose, embutramide, T-61, COc, CO2c, gunshotc

Finfish

S6.2: Immersion in buffered benzocaine or benzocaine hydrochloride, isoflurane, sevoflurane, metomidate, quinaldine sulfate, buffered tricaine methanesulfonate, 2-phenoxyethanol, injected pentobarbital, rapid chilling (appropriate zebrafish/research setting)

S6.2: Eugenol, isoeugenol, clove oil, CO2-saturated water (aquarium-fish facilities/fisheries), decapitation/cervical transection/manually applied blunt force trauma followed by pithing, rapid chilling followed by adjunctive method (aquarium-fish facilities), maceration (research setting)

Equids

S4: IV barbiturates

S 4: Penetrating captive bolt, gunshot

Marine mammals

S7.4: Injected barbiturates (captive)

S7.4: Inhaled anesthetics (captive)

S7.6: Gunshot, manually applied blunt force trauma, implosive decerebration (free ranging)

Nonhuman primates

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

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

Poultry

S3.4: Injected barbiturates and anesthetic overdose

S3.4: CO2, CO, N2, Ar, 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

Reptiles

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

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: Gunshot, penetrating captive bolt

Swine

S3.3: Injected barbiturates

S3.3: CO2, CO, N2, Ar, gunshot, electrocution, nonpenetrating captive bolt, manually applied blunt force trauma

Reprinted, with permission, from the AVMA Guidelines on Euthanasia 2013 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/KB/Policies/Documents/euthanasia.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.

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* This is the Veterinary Version. *