When it becomes necessary to euthanize or perform humane killing of laboratory animals, it is important to choose methods that are quick, effective, and minimize pain and distress. The selection of the appropriate method may depend on factors such as the species, size, and specific requirements of the animal. Here are some common humane killing methods for lab animals:

Humane killing is a scientifically approved method in which an animal is killed without infringing or causing them to feel any pain whatsoever.

Euthanasia
Euthanasia means the humane killing of an animal accomplished by
a method that produces rapid unconsciousness and subsequent death
without evidence of pain or distress, or a method that utilizes anesthesia produced by an agent that causes painless loss of consciousness and subsequent death.

The choice of a method depends on species, age, availability of restraint, skill of the individuals performing euthanasia and other considerations. In a research setting, the method of euthanasia must be consistent with the research goals.

Whenever an animal’s life is to be taken, it should be treated with the highest respect. The method causing the least animal pain and distress should be used. The killing method should:

1. Cause rapid loss of consciousness, followed by cardiac or respiratory arrest and ultimate loss of brain function
2. Require minimum restraint of the animal
3. Be appropriate for the species, age and health of the animal

Only trained and competent personnel are allowed to carry out humane killing and death of the animal must be verified following humane killing.

1.   Chemical methods

a. Inhalation of carbon dioxide (Co₂)

This method is suitable for small rodents and birds; animals should be exposed to an atmosphere of 30 % CO₂ (to ensure loss of consciousness) which is then increased to 70% to kill the animals. This may be achieved by placing the animal in an air-filled container and then allowing the gas to flow into it so that the concentration rises to at least 70% and is maintained there for at least 3 minutes. Animals may be left in the container until rigor mortis is observed, or they may be removed and death ensured by exsanguination or dislocation of the neck, and confirmed dead.

b. Inhalation of volatile anesthetic

It is suitable for small rodents where the animal is exposed to a volatile anesthetic substance leading to its overdose and hence death. When using an anesthetic overdose there should be no contact between the animal and the anesthetic in its liquid form. The procedure should always be carried out in a fume cupboard or a well-ventilated area so that the operator is not subjected to prolonged exposure to the vapor fumes.

c. Injection of anesthetic

This method is Suitable for all species. It is a method of choice for larger species; an overdose of anesthetic substance should be administered intravenously or intraperitoneally and be sufficient to ensure rapid unconsciousness and death.

2 .Exsanguination
Exsanguination is the action or the process of draining or losing blood. The animal is first rendered insensitive to pain by various methods e.g. sedation or aesthetic

3. Physical methods

• Dislocation of cervical vertebrae – suitable for small rodents, small rabbits and larger birds. The animal`s head is restrained between   the fingers and then twisted  by turning it backwards  so as to break the spinal cord
• Concussion by striking the back of the animal’s head. This method is restricted to animals that are handled easily and that have relatively thin skulls, i.e. small rodents and smaller birds.
• Decapitation used for rodents where other methods would be unsuitable. It is the complete removal of the head from the body. This method must only be carried out using a specially designed and properly maintained guillotine.
• Pithing

The soft skull of the animal is pierced using a sharp needle then stirring up the brain. Mostly done on frogs and toads

Immersing the animal in the already boiled and cooled water

The animal is dropped into oxygen free water and therefore the animal will die slowly due to lack of oxygen. This can be done on frogs, fish reptiles etc.

NB: It is essential to ensure that the animal is dead before disposal. The animals must be kept and observed for several minutes after all signs of life have ceased. Alternatively, the animal’s neck should be dislocated or the animal may be exsanguinated. Preferably, animals should be disposed of on site by incineration. If this is not possible, care should be taken to prevent exposure of the carcasses to the public. Infected, toxic or radioactive carcasses must be disposed of in such a manner that they do not present a hazard.