The methods of euthanasia 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 other acceptable methods are used in different situations.
Intravenous anesthetic Upon administration of intravenous anesthetic, unconsciousness,
respiratory, then
cardiac arrest follow rapidly, usually within 30 seconds. The two-stage process that some veterinarians use includes a first shot that is a
sedative to make the animal more comfortable, and then a second shot that euthanizes the animal. This allows the owner the chance to say goodbye to a live pet without their emotions stressing the animal. It also greatly mitigates any tendency toward spasm and other involuntary movements, 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. 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. Anecdotal reports that long-term use of
phenylbutazone increases the risk of this reaction are unverified. After an animal has died, it is not uncommon for the body to exhibit postmortem jerks or a sudden bladder or bowel outburst. This is caused by the muscles of the deceased animal's body relaxing.
Inhalants 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 inhalation of an anesthetic. Carbon dioxide is often used on its own for the euthanasia of wild animals. 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. 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 euthanasia of small rodents.
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.
Nitrogen is effective, although some young animals are more resistant to the effects, and it currently is not widely used. The use of gas chambers is not the most humane form of euthanasia, as it can take up to 20 minutes to fully euthanize the animal. If the chambers are not calibrated correctly or the animal is ill, the process is only delayed further, which can cause more harm to the animal.
Cervical dislocation Cervical dislocation, or displacement (breaking or fracturing) of the neck, is an older and less common method of killing small animals such as mice. When performed properly, it is intended to cause a death that is as painless as possible and has no cost or equipment involved. The handler must know the proper method for executing the movement that will cause cervical displacement. Without proper training and method education, there is a risk of not causing death, which can cause severe pain and suffering. It is unknown how long an animal remains conscious, or the level of suffering it experiences after a proper snap of the neck, which is why it has become less common and is often replaced 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. Concerning state and federal laws, one of the most humane forms of euthanizing animals is through the injection of Sodium Pentobarbital. This is typically the second shot that is administered after a sedative when euthanizing animals. While
intraperitoneal injection is fully acceptable (although it may take up to 15 minutes to take effect in dogs and cats
Shooting This can be a means of euthanasia for large animals—such as horses, cattle, and deer—if performed properly. This may be performed by means of: ;
Firearms: The risks are minimal if carried out by skilled personnel in a suitable location. ;
Captive bolt gun: == Reasons ==