Whilst animal research still happens many animals will continue to lose their lives for the purpose of science. For the most part this will be planned into experiments before animal research licenses are granted. The current regulatory framework defines the methods that may be used to achieve this.

Why do animals require euthanasia?

Animals are euthanised in a research capacity for a number of reasons that can be split into two categories: planned and emergency. Planned reasons for euthanasia include terminating a procedure as part of a humane endpoint, killing surplus animals that are not needed or have undesirable characteristics, and to harvest organs and tissues for ex vivo work. Emergency reasons for euthanasia include when an animal is in severe pain or distress which cannot be alleviated in another way.

What is schedule 1?

Schedule 1 is a list of humane methods of and approved means of confirming that the animals are deceased.

Schedule 1 killings are not regulated procedures and therefore do not require a project license to perform. They must, however, be performed by a trained and competent person whose name is retained on the establishment’s schedule 1 register. Conducting a schedule 1 killing is a two-step process that must involve an approved method of killing and an approved method of confirmation. If an animal is killed in any other manner, or death is not confirmed by an approved method, the killing cannot be considered a schedule 1 killing and will require a project license before performing as a regulated procedure.

Table A methods

Table A of schedule 1 outlines the methods of killing that are suitable for any animal other than foetal, larval, or embryonic forms – meaning any animal that has been born.

There are 5 methods in table A:

1) Overdose of anaesthetic

This can be used for any species of animal, however, the type of anaesthetic used and the route of administration must be appropriate for the size and species of the animal.

2) Exposure to carbon dioxide gas in a rising concentration

This involves placing the animal into a secure chamber and filling it gradually with carbon dioxide until the animal is unconscious. This is suitable for rodents, rabbits, and birds up to 1.5kg.

3) Dislocation of the neck

This is performed by asserting pressure to the base or side of an animal’s neck, usually by using a thumb and forefinger, or a metal instrument such as a rod. This method is suitable for rodents up to 500g, rabbits up to 1kg, and birds up to 1kg. However, for rodents and rabbits over 150g and birds over 250g, sedatives should be used prior to performing this method.

4) Concussion of the brain by striking the cranium

This involves performing a sharp blow to the head of an animal. This is suitable for rodents and rabbits up to 1 kg, birds up to 250g, amphibians and reptiles up to 1kg, and fishes of any type and weight. It is also specified that with amphibians, reptiles, and fish, there . This method is less commonly used in mammal species but is still common practice with fish.

5) Destruction of the brain by free bullet using an appropriate rifle, gun or ammunition, or captive bolt or electrical stunning followed by destruction of the brain or draining of blood before the return of consciousness

These methods may only be carried out by a registered veterinary surgeon or by a license holder under the Welfare of Animals at the Time of Killing (England) Regulations 2015, Welfare of Animals at the Time of Killing (Wales) Regulations 2014, or Welfare of Animals at the Time of Killing (Scotland) Regulations 2012. These are only suitable for ungulates (hoofed mammals).

Table B methods

Table B of schedule 1 outlines the methods of killing that are suitable for foetal, larval, and embryonic forms of animals.  

There are 4 methods in this table: 

1) Overdose of anaesthetic 

As with the animals covered in table A, anaesthetic is quick at rendering animals unconscious, but the route and type of anaesthetic used must be appropriate for the size, stage of development, and the species of animal. 

2) Refrigeration, disruption of membranes, maceration, or exposure to carbon dioxide 

Under schedule 1, it is specified that the apparatus used for maceration must be approved under appropriate slaughter legislation. It is also specified that exposure to carbon dioxide must be performed at near 100% concentration until the animal is deceased. These methods are only suitable for birds and reptiles. 

3) Cooling of foetuses followed by immersion in cold tissue fixative 

Performing cooling and immersion in a cold tissue fixative allows the foetus to be killed, but their tissues to be preserved allowing the tissues to remain useful for scientific purposes. This is only suitable for mice, rats, and rabbits.

4) Decapitation 

As the name suggests, this method involves severing the head of the animals. This method is only suitable for mammals and birds up to 50g. 

Confirmation methods

An approved confirmation method must follow an approved killing method for an animal’s death to be considered a schedule 1 kill. Approved confirmation methods are: 

• Confirmation of permanent cessation of circulation. This is usually confirmed by cutting an animal’s femoral artery 

• Destruction of the brain 

• Dislocation of the neck 

• Exsanguination (draining of blood) 

• Confirmation of the onset of rigor mortis. Rigor mortis is the stiffening of muscles after death. This method is not commonly used within research as it requires waiting for a period of time to ensure an animal is dead. 

• Instantaneous destruction of the body in a macerator. This is also uncommon in a research capacity unless needing to euthanise large numbers of surplus animals, as it completely destroys any parts of the animal that could have been utilised for a scientific purpose. 

What needs to be considered when choosing a method? 

Several factors need to be considered when selecting which method under schedule 1 to use: 

Scientific outcome 

• The method chosen must be appropriate for the scientific outcome that is desired. This could include the type of sample that needs to be taken from an animal, what is being measured in terms of data, and how long death will take to occur.  

Legislation 

• Schedule 1 of ASPA outlines which methods are suitable for which species, weight, and stage of development. This should be the first port of call when choosing a method and a method should only be selected if it is explicitly stated that it is suitable for the animal requiring euthanasia.  

What is best for the animals? 

• The welfare of the animals being euthanised is vitally important and there are many known stressors to animals that can be reduced depending on the method selected. Known stressors include: 
  • The level of pain that will be experienced 
  • Transporting the animal from their housing to the area where killing will take place 
  • Capturing the animal  
  • Handling the animal 
  • Restraining the animal 
  • Separating the animal from other animals within its housing if they are a social species. Euthanasia must be performed out of sight, sound, and smell of other animals on the premises
  • Exposure to an unfamiliar location 

Of the stressors named above, all except the level of pain experienced are likely to be experienced before a schedule 1 killing physically taking place. 

• The most humane method of killing should always be considered as a priority, however, it is important to note that the quickest method does not always equal the most humane. The quicker methods, such as neck dislocation have a higher risk of injury, pain, and distress should the method be carried out incorrectly. 
• The physical constraints of whoever is performing the euthanasia must also be considered to ensure that a method can be performed practically and efficiently.