Euthanasia

Tables of acceptable and conditionally acceptable methods

Differences between the 1993 and 2000 reports

Acceptable methods by species

	Barbiturates	CO₂	Inhalant anesthetics	CO	Microwave	MS222	Double pith	Other
NHPs Ruminants^1,3 Horses^1,3	X							KCl³ Captive bolt¹
Swine^1,3	X	X						KCl³ Captive bolt¹
Sea mammals²	X							Etorphine²
Free-ranging wildlife³	X		X					KCl³
Reptiles	X	X	X
Dogs³ Cats³ Rabbits³ Fur animals³ Birds⁴ Zoo animals³	X	X	X	X				KCl³Gunshot⁴
Rodents^3,5 Other small mammals^3,5	X	X	X	X	X			KCl³Microwave⁵
Amphibians	X	X	X	X		X	X
Fish	X	X	X			X

Notes:
1- Can also use captive bolt or KCl in conjunction with general anesthesia
2- Can also use etorphine or carfentanil in sea mammals
3- Can also use KCl in conjunction with surgical plane anesthesia
4- Can also use gunshot for free-ranging birds
5- Microwave at 1.3-10kW is the most effective method to fix brain tissue in vivo for subsequent assay of enzymatically labile chemicals.

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Conditionally-acceptable methods of euthanasia

	Nitrogen, Argon	Captive bolt	Gunshot	Electrocution	Decapitation	Chloral hydrate	Cervical Dislocation	Other
NHPs	X							Inhalant anesthetics, CO₂, CO
Ruminants			X	X		X¹
Horses			X	X		X¹
Swine			X	X		X¹		Inhalant anesthetics, CO, blow to head⁵
Sea mammals <4m			X
Free-ranging wildlife	X	X	X					CO₂, CO, kill traps
Reptiles		X	X		X⁴
Dogs	X	X		X
Cats	X
Rabbits	X	X			X		X³
Fur animals	X			X²
Birds	X				X		X	Thoracic compression
Zoo animals	X	X	X
Rodents, other small mammals	X				X		X³	Metofane, ether
Amphibians		X	X		X⁴
Fish					X⁴

1- Horses, ruminants and swine must be sedated prior to chloral hydrate euthanasia
2- In fur animals, follow electrocution with cervical dislocation
3- Rabbits must be <1 kg and rats <200gm for cervical dislocation
4- Reptiles, fish and amphibians may be decapitated and pithed, or stunned and decapitated or pithed
5- Only swine <3 weeks of age may be killed by a blow to the head

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Differences between the 1993 and 2000 Euthanasia Panel Reports

In this newest version of the report{4345}, the panel has updated information on euthanasia of animals in research and animal care and control facilities; expanded information on ectothermic, aquatic, and fur-bearing animals; added information on horses and wildlife; and deleted methods or agents considered unacceptable.

Changes that might impact animal research:

	Inhalant anesthetics are listed in order of preference; halothane, enflurane, isoflurane, sevoflurane, methoxyflurane, and desflurane.
	"Ether should only be used in carefully controlled situations in compliance with state and federal occupational health and safety regulations. It is conditionally acceptable."
	"Compressed CO₂gas in cylinders is the only recommended source of carbon dioxide because the inflow to the chamber can be regulated precisely. Carbon dioxide generated by other methods such as from dry ice, fire extinguishers, or chemical means (e.g., antacids) is unacceptable."
	"When other methods cannot be used, an accurately delivered gunshot is a conditionally acceptable method of euthanasia."
	Cervical dislocation - "In research settings, this technique should be used only when scientifically justified by the user and approved by the Institutional Animal Care and Use Committee."
	Decapitation - "This technique is conditionally acceptable if performed correctly, and it should be used in research settings when its use is required by the experimental design and approved by the Institutional Animal Care and Use Committee."
	"Cardiopulmonary compression is not appropriate for laboratory settings, for large or diving birds, or for other species" (however, it is okay for wild birds in field settings).
	"For some species, such as frogs, with anatomic features that facilitate easy access to the central nervous system, pithing may be used as a sole means of euthanasia, but an anesthetic overdose is a more suitable method."
	"It has been suggested that, when using physical methods of euthanasia in ectothermic species, cooling to 4° C will decrease metabolism and facilitate handling, but there is no evidence that whole body cooling reduces pain or is clinically efficacious... Immobilization of reptiles by cooling is considered inappropriate and inhumane even if combined with other physical or chemical methods of euthanasia. Snakes and turtles, immobilized by cooling, have been killed by subsequent freezing. This method is not recommended."

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Carbon Dioxide

This method is acceptable for rats, mice, guinea pigs, chickens, rabbits, mink, swine (unconsciousness prior to slaughter), burrowing and diving animals, fish, reptiles, and amphibians. There is some concern that carbonic acid, which is formed when CO₂ comes in contact with mucous membranes, stimulates nociceptors. Some animals require more care than others when using carbon dioxide. Higher concentrations or longer times may be required for 1-day-old chicks since they are accustomed to an environment in the egg containing 14% carbon dioxide. Burrowing animals (Oryctolagus), fish, and diving animals have mechanisms for coping with hypercapnia. Reptiles and amphibians may simply breathe too slowly for the carbon dioxide to work effectively.

Only carbon dioxide in compressed gas cylinders may be used for euthanasia, since this provides a means of controlling the concentration and flow. Dry ice, antacids, and fire extinguishers are not acceptable sources. The gas flow should displace 20% of the chamber volume per minute. The chamber can be prefilled with 70% or more in species in which this has not been shown to cause distress (not named).

Addition of oxygen to the carbon dioxide, according to the AVMA, offers no advantage for euthanasia, and may actually prolong the time to death and complicate determination of consciousness. Others have observed that adding oxygen seems to decrease the negative effects of carbon dioxide on behavior, for example in a ratio of 70% CO₂: 30% O₂. An experiment in mice comparing several ratios showed that time to recumbency was the same, but time to death was prolonged in mice exposed to 70:30 mixture (40 seconds to death with 100% CO₂, but 280 seconds with 70:30). There were differences in T cell subpopulations depending upon the concentration of carbon dioxide used, perhaps due to them going into the spleen. There were no differences in hormone levels (LH, FSH, prolactin).{4180}

Comments? Send an email to janet.rodgers@vet.ox.ac.uk