The term euthanasia was derived from the Greek terms eu meaning ‘good’ and thanatos meaning ‘death’. The definition of euthanasia found in the Guide is “the act of killing animals by methods that induce rapid unconsciousness and death without pain or distress.”
The PHS Policy and the AWRs require that the IACUC review and approve methods of euthanasia. These methods must be consistent with the latest recommendations of the American Veterinary Medical Association (AVMA) Panel on Euthanasia, unless scientifically justified in writing by the investigator and approved by the IACUC. Some of the criteria used to determine acceptable methods are the ability to induce rapid unconsciousness and death with a minimal amount of pain, distress, anxiety, and apprehension; irreversibility; reliability; compatibility with species, age and health status; compatibility with research objectives; and with regard for the safety of and emotional effect on observers or operators.
Certain species may exhibit fearful behavior, distress vocalizations, or the release of pheromones when frightened (during induction of unconsciousness). Because this may cause apprehension and anxiety in other animals, they should not be present when individual animal euthanasia is performed.
While all methods of euthanasia must be reviewed and approved by the IACUC, the following categories are contained in the AVMA report.
(Require IACUC Approval and Scientific Justification)
CO2 inhalation is the most common method of euthanasia for laboratory animals. The NIH has established guidelines through a PHS Policy for using CO2. These guidelines are: Although CO2 is generally considered an acceptable euthanasia agent for small laboratory animals when properly administered, its acceptability is predicated on the following:
Institutions must ensure that all individuals responsible for administering CO2 euthanasia are appropriately qualified and monitored, and that they adhere to IACUC-approved protocols and institutional policies.
Chambers must not be overcrowded. In this regard, it is important to also consider that mixing unfamiliar or incompatible animals in the same container may be distressful.
Compressed CO2 in cylinders is the only AVMA Panel-recommended source of CO2 for euthanasia purposes.
Fetuses up to 14 days in gestation are not sensitive to inhalant anesthetics, including CO2. Euthanasia of the mother or removal of the fetus should result in rapid death.
Fetuses 15 days in gestation to birth are also not sensitive to the affects of inhalant anesthetics. Decapitation with a sharp instrument, cervical dislocation or immersion in liquid nitrogen are acceptable methods of euthanasia for this group.
Neonates up to 14 days of age may be euthanized by injection of a chemical anesthetic, decapitation, or cervical dislocation. Pups older then one day should be anesthetized prior to immersion in liquid nitrogen or immersed in a fixative. Anesthesia may be induced by inhalant or injectable means, or hypothermia if pups are less than 6 days old.
Inhalant anesthetics are relatively ineffective on amphibians and reptiles because of their low oxygen requirements.
Intraperitoneal injection of pentobarbital is an acceptable and effective method of euthanasia for amphibians, turtles, and snakes. Tricaine methane sulfonate (MS222) or benzocaine hydrochloride may be added to the water of fish and amphibians to produce anesthesia and death at appropriate concentrations and exposure times.
Stunning followed by decapitation, pithing, or some other method that ensures death is also acceptable in poikilotherms. Frogs and toads may be euthanized by pithing of the brain and spinal cord (double pithing).
All approved methods of euthanasia should be performed in a professional and compassionate manner by skilled and experienced individuals. Death must be confirmed after euthanasia and prior to disposal. Appropriate dosing of chemicals, proper concentration and exposure times to CO2, and skillful performance of physical methods are required to prevent unintended recovery of animals. Unintended recovery of animals after euthanasia is a serious deviation from PHS Policy and the Guide, and as such, is a reportable occurrence of noncompliance. The IACUC must be notified of any such occurrence.