Animal euthanasia

This article is about mercy killing of animals. For compassionate death in humans, see Euthanasia.

Animal euthanasia (euthanasia from Greek: εὐθανασία; "good death") is the act of putting an animal to death or allowing it to die by withholding extreme medical measures. Reasons for euthanasia include incurable (and especially painful) conditions or diseases,[1] lack of resources to continue supporting the animal, or laboratory test procedures. Euthanasia methods are designed to cause minimal pain and distress. Euthanasia is distinct from animal slaughter and pest control although in some cases the procedure is the same.

In domesticated animals, this process is commonly referred to by euphemisms such as "put down", "put to sleep", or "put out of his/her/its misery".


The methods of anesthesia can be divided into pharmacological and physical methods. Acceptable pharmacological methods include injected drugs and gases that first depress the central nervous system and then cardiovascular activity. Acceptable physical methods must first cause rapid loss of consciousness by disrupting the central nervous system. The most common methods are discussed here, but there are other acceptable methods used in different situations.[2]

Intravenous anesthetic

Unconsciousness, respiratory then cardiac arrest follow rapidly, usually within 30 seconds.[3] Observers generally describe the method as leading to a quick and peaceful death.

For companion animals euthanized in animal shelters, 14 states in the US now prescribe intravenous injection as the required method. These laws date to 1990, when Georgia's "Humane Euthanasia Act" became the first state law to mandate this method. Before that, gas chambers and other means were commonly employed. The Georgia law was resisted by the Georgia Commissioner of Agriculture, Tommy Irvin, who was charged with enforcing the act. In March 2007, he was sued by former State Representative Chesley V. Morton, who wrote the law, and subsequently ordered by the Court to enforce all provisions of the Act.[4]

Some veterinarians perform a two-stage process: an initial injection that simply renders the pet unconscious and a second shot that causes death. This allows the owner the chance to say goodbye to a live pet without their emotions stressing the pet. It also greatly mitigates any tendency toward spasm and other involuntary movement which tends to increase the emotional upset that the pet's owner experiences.

For large animals, the volumes of barbiturates required are considered by some to be impractical, although this is standard practice in the United States.[5] For horses and cattle, other drugs may be available. Some specially formulated combination products are available, such as Somulose (Secobarbital/Cinchocaine) and Tributame (Embutramide/Chloroquine/Lidocaine), which cause deep unconsciousness and cardiac arrest independently with a lower volume of injection, thus making the process faster, safer, and more effective.

Occasionally, a horse injected with these mixtures may display apparent seizure activity before death. This may be due to premature cardiac arrest. However, if normal precautions (e.g., sedation with detomidine) are taken, this is rarely a problem.[6] Anecdotal reports that long-term use of phenylbutazone increases the risk of this reaction are unverified.

After the animal has expired, it is not uncommon for the body to have posthumous body jerks, or for the animal to have a sudden bladder outburst.


Gas anesthetics such as isoflurane and sevoflurane can be used for euthanasia of very small animals. The animals are placed in sealed chambers where high levels of anesthetic gas are introduced. Death may also be caused using carbon dioxide once unconsciousness has been achieved by inhaled anaesthetic.[7] Carbon dioxide is often used on its own for euthanasia of wild animals.[8] There are mixed opinions on whether it causes distress when used on its own, with human experiments lending support to the evidence that it can cause distress and equivocal results in non-humans.[9] In 2013, the American Veterinary Medical Association (AVMA) issued new guidelines for carbon dioxide induction, stating that a flow rate of 10% to 30% volume/min is optimal for the humane euthanization of small rodents.[10]

Carbon monoxide is often used, but some states in the US have banned its use in animal shelters: although carbon monoxide poisoning is not particularly painful, the conditions in the gas chamber are often not humane.[11] Nitrogen has been shown to be effective, although some young animals are rather resistant[12] and it currently is not widely used.

Cervical dislocation

Cervical dislocation, or displacement of the neck, is an older yet less common method of killing small animals such as mice. Performed properly it is intended to cause as painless death as possible and has no cost or equipment involved. The handler must know the proper method of executing the movement which will cause the cervical displacement and without proper training and method education there is a risk of not causing death and can cause severe pain and suffering. It is unknown how long an animal remains conscious, or the level of suffering it goes through after a correct snapping of the neck, which is why it has become less common and often substituted with inhalants.

Intracardiac or intraperitoneal injection

When intravenous injection is not possible, euthanasia drugs such as pentobarbital can be injected directly into a heart chamber or body cavity.

While intraperitoneal injection is fully acceptable (although it may take up to 15 minutes to take effect in dogs and cats[7]), an intracardiac (IC) injection may only be performed on an unconscious or deeply sedated animal. Performing IC injections on a fully conscious animal in places with humane laws for animal handling is often a criminal offense.[13]


Captive bolt device

This can be an appropriate means of euthanasia for large animals (e.g., horses, cattle, deer) if performed properly. This may be performed by means of:

Free bullet 
Traditionally used for shooting horses. The horse is shot in the forehead with the bullet directed down the spine through the medulla oblongata, resulting in instant death.[14] The risks are minimal if carried out by skilled personnel in a suitable location.
Captive bolt 
Commonly used for cattle and other livestock. The bolt is fired through the forehead causing massive disruption of the cerebral cortex. In cattle, this stuns the animal, though if left for a prolonged period it will die from cerebral oedema. Death should therefore be rapidly brought about by pithing or exsanguination. Horses are killed outright by the captive bolt, making pithing and exsanguination unnecessary.[15]

Reasons for euthanasia

The reasons for euthanasia of pets and other animals include:

Lethal chamber in the Royal London Institute and Home for Lost and Starving Cats

Small animal euthanasia is typically performed in a veterinary clinic or hospital or in an animal shelter and is usually carried out by a veterinarian or a veterinary technician working under the veterinarian's supervision. Often animal shelter workers are trained to perform euthanasia as well. Some veterinarians will perform euthanasia at the pet owner's homethis is virtually mandatory in the case of large animal euthanasia. In the case of large animals which have sustained injuries, this will also occur at the site of the accident, for example, on a racecourse.

Some animal rights organizations support animal euthanasia in certain circumstances and practice euthanasia at shelters that they operate.[16]


Many pet owners choose to have their pets cremated or buried after the pet is euthanized,[17] and there are pet funeral homes that specialize in animal burial or cremation.[18] Otherwise, the animal facility will often freeze the body and subsequently send it to the local landfill.[19]

In some instances, animals euthanized at shelters or animal control agencies have been sent to meat rendering facilities[20][21][22] to be processed for use in cosmetics, fertilizer, gelatin, poultry feed, pharmaceuticals and pet food.[23] It was proposed that the presence of pentobarbital in dog food may have caused dogs to become less responsive to the drug when being euthanized.[24] However, a 2002 FDA study found no dog or cat DNA in the foods they tested, so it was theorized that the drug found in dog food came from euthanized cattle and horses. Furthermore, the level of the drug found in pet food was safe.[25]

See also

Wikimedia Commons has media related to Animal euthanasia.


  1. 2000 Report of the AVMA Panel on Euthanasia
  2. 1 2 Close B, Banister K, Baumans V, Bernoth EM, Bromage N, Bunyan J, Erhardt W, Flecknell P, Gregory N, Hackbarth H, Morton D, Warwick C (1996). "Recommendations for euthanasia of experimental animals: Part 1". Laboratory animals. 30 (4): 293–316 (295). doi:10.1258/002367796780739871. PMID 8938617.
  3. UK Veterinary Medicines Directorate Product Notes for 20% Pentobarbital solution.
  4. "Archived copy" (PDF). Archived from the original (PDF) on 4 March 2016. Retrieved 2016-02-07.
  5. "Euthanasia Guidelines" (PDF). AAEP. 207. Archived from the original (PDF) on 26 June 2008. Retrieved 19 June 2008.
  6. NOAH Compendium of Data Sheets for Animal Medicines 2005
  7. 1 2 "Laboratory Animal Euthanasia" (DOC). Australian National University. Archived from the original on 19 August 2007. Retrieved 30 November 2007.
  8. Animal Euthanasia Information - Carbon doxide gas (Internet Center for Wildlife Damage Management
  9. Conlee KM, Stephens ML, Rowan AN, King LA (April 2005). "Carbon dioxide for euthanasia: concerns regarding pain and distress, with special reference to mice and rats". Lab. Anim. 39 (2): 137–61. doi:10.1258/0023677053739747. PMID 15901358.
  10. 2013 AVMA Guidelines for the Euthanasia of Animals
  11. Animal Gas Chambers Draw Fire in U.S. - National Geographic
  12. Quine JP, Buckingham W, Strunin L (September 1988). "Euthanasia of small animals with nitrogen; comparison with intravenous pentobarbital". Can. Vet. J. 29 (9): 724–6. PMC 1680841Freely accessible. PMID 17423118.
  13. Calif. Penal Code 597u (a)(2)
  14. Tom J. Doherty, Alex Valverde, Manual of Equine Anaesthesia and Analgesia, Blackwell Publishing 2006 (p. 352)
  15. C.J. Laurence, "Animal welfare consequences in England and Wales of the 2001 epidemic of foot and mouth disease", Rev. sci. tech. Off. int. Epiz, 2002, 21 (3), 863–868)
  16. "Animal Rights Uncompromised:'No-Kill' Shelters", PETA, Retrieved 26 June 2010; "A reply from PETA to a letter inquiring about its euthanization decisions",, Retrieved 26 June 2010.
  17. Allen, Moira Anderson (2002). "The Final Farewell: How to Handle a Pet's Remains". Pet Loss Support Page. Retrieved 9 June 2010.
  18. Porstner, Donna (15 April 2004). "Pet funeral home offers services for grieving owners". Retrieved 9 June 2010.
  19. "What Do Animal Shelters Do with the Bodies of Dead Pets?". Knoji: Consumer Knowledge. 21 February 2011. Retrieved May 21, 2014.
  20. Becker, Geoffrey S. (17 March 2004). "Animal Rendering: Economics and Policy" (PDF). The National Agricultural Law Centre: Congressional Research Service Reports. Retrieved 9 June 2010.
  21. Smith, Van (3 November 1998). "Rendering Unto Oprah". Baltimore City Paper. Retrieved 9 June 2010.
  22. "Chapter 9, Food and Agricultural Industries" (PDF). Compilation of Air Pollutant Emission Factors. Retrieved 9 June 2010.
  23. Simon, Stephanie (27 January 2002). "Pet Food Report Leads to Pile-Up At Animal Shelters – Rendering Plant Stops Taking Carcasses". Washington Post. p. A14.
  24. Myers, Michael (2004). "CVM Scientists Develop PCR Test to Determine Source of Animal Products in Feed, Pet Food". FDA Veterinarian Newsletter. XIX (1). Retrieved 8 June 2010.
  25. "Report on the risk from pentobarbital in dog food". US Food and Drug Administration. 28 February 2002. Archived from the original on 30 April 2008. Retrieved 9 June 2010.

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