Summary of Conditionally Acceptable Agents and Methods of Euthanasia - Characteristics and Modes of Action
Agents Classification Mode of action Rapidity Ease of performance Safety  Species suitability Efficacy and comments
Blow to head Physical damage to brain Direct concussion of brain tissue Rapid Requires skill, adequate restraint, and appropriate force Safe Young pigs < 3 weeks old Must be properly applied to be humane and effective
Carbon dioxide (bottled gas only) Hypoxia due to depression of vital centers Direct depression of cerebral cortex, subcortical structures and vital centers; direct depression of heart muscle Moderately rapid Used in closed container Minimal hazard Nonhuman primates, free ranging wildlife Effective, but time required may be prolonged in immature and neonatal animals
Carbon monoxide (bottled gas only) Hypoxia Combines with hemoglobin, preventing its combination with oxygen Moderate onset time, but insidious so animal is unaware of onset Requires appropriately maintained equipment Extremely hazardous, toxic and difficult to detect Nonhuman primates, free ranging wildlife Effective, acceptable only when equipment is properly designed and operated
Cervical dislocation Hypoxia due to disruption of vital centers Direct depression of brain Moderately rapid Requires training and skill Safe Poultry, birds, lab mice, and rats (< 200 g) or rabbits (<1 kg) Irreversible. Violent muscle contractions can occur after cervical dislocation
Chloral hydrate Hypoxia from depression of respiratory center Direct depression of brain Rapid Personnel must be skilled perform IV injection Safe Horses, ruminants and swine Animals should be sedated prior to administration
Decapitation Hypoxia due to disruption of vital centers Direct depression of brain Rapid Requires training and skill Guillotine pose potential employee injury hazard Laboratory rodents, small rabbits, birds, some fish, amphibians, and reptiles (latter 3 with pithing) Irreversible. Violent muscle contraction can occur after decapitation
Electrocution Hypoxia Direct depression of brain and cardiac fibrillation Can be rapid Not easily performed in all instances Hazardous to personnel Used primarily in foxes, sheep, swine, mink (with cervical dislocation), ruminants, animals <5 kg Violent muscle contractions occur at same time as loss of unconsciousness
Gunshot Hypoxia due to disruption of vital centers Direct concussion of brain tissue Rapid Requires skill and appropriate firearm May be dangerous Large domestic and zoo animals, reptiles, amphibians, wildlife, cetaceans (<4 meters long) Instant unconsciousness, but motor activity may continue
Inhalant anesthetics Hypoxia due to depression of vital centers Direct depression of cerebral cortex, subcortical structures, and vital centers Moderately rapid onset of anesthesia; excitation may develop during induction Easily performed with closed container; can be administered to large animals by means of a mask Must be properly scavenged or vented to minimize exposure to personnel Nonhuman primates, swine Highly effective provided that subject is sufficiently exposed
Nitrogen, Argon Hypoxia Reduces partial pressure of oxygen available to blood Rapid Use closed chamber with rapid filling Safe if used with ventilation Cats, small dogs, birds, rodents, rabbits, other small species, mink, zoo animals, nonhuman primates, free ranging wildlife Effective except in young and neonates; an effective agent, but other methods preferable
Penetrating captive bolt Physical damage to brain Direct concussion of brain tissue Rapid Requires skill, adequate restraint, and proper placement of captive bolt Safe Dogs, rabbits, zoo animals, reptiles, amphibians, free ranging wildlife Instant loss of consciousness but motor activity may continue
Pithing Hypoxia due to disruption of vital centers, physical damage to brain Trauma of brain and spinal cord tissue Rapid Easily performed, but requires skill Safe Some ectotherms Effective, but death not immediate unless brain and spinal cord are pithed
Thoracic compression Hypoxia and cardiac arrest Physical interference with cardiac and respiratory function Moderately rapid Requires training Safe Small to medium sized free ranging birds Apparently effective
               

From 2000 Report of the AVMA Panel on Euthanasia,.