The term humane endpoints is a phrase used in animal research regulation. In this article we explain what this phrase means in current legislation and regulation.

Humane endpoints must be identified in all project licenses for animal research, and identify the earliest point at which a procedure will be ended to minimise pain, distress or discomfort, whilst allowing the scientific objectives of the research to be met. While humane endpoints often result in the euthanasia of an animal, they are set as an endpoint to a procedure, not an animal, and can also be applied in the form of predetermined pain relief. Under the Animals (Scientific Procedures) Act 1986 (ASPA), a humane endpoint is defined as “a clear, predictable and irreversible criteria that allows early termination of a procedure before an animal experiences harm that is not authorised or scientifically justified.”  They also allow for death as an endpoint of a procedure to be avoided as much as possible.  

What should be considered when establishing a humane endpoint? 

Humane endpoints must be pre-determined before an experiment begins and outlined in a project license application. They should not be decided on an ad-hoc basis, however they should be monitored and reviewed throughout an experiment, being changed if required. If, in the UK, changes are required to surpass the current humane endpoints stated under a project license, the Home Office must be contacted as soon as possible, who may authorise a temporary 14-day higher severity level allowing the humane endpoint limited to be exceeded. A harm benefit analysis will take place during the 14-day period, and the project license will be permanently amended if the benefits outweigh the harms. This will only be done if a reason for this can be justified.  

When establishing what a humane endpoint will consist of, the level of pain and discomfort the given procedure will likely cause must be considered. This will affect the frequency of observations for monitoring endpoints and what indicators to look for. Options surrounding treatment or euthanasia must also be considered. This will involve whether treatment is enough as an endpoint, or whether euthanasia is the preferred option depending on the procedures taking place, as well as what types of treatments or methods of euthanasia will be used. In the UK, a schedule 1 killing method will likely be used to euthanise an animal. Information on how humane endpoints were monitored, recorded, and applied throughout an experiment should be included when publishing the results of the study. This helps build up the literature on humane endpoints in research. 

In order to determine humane endpoints, researchers must already be aware of the normal behaviour and physiology of the animals being used, progression of indicators for the procedures taking place, and at what point a humane endpoint will be applied. If, particularly with regards to the progression of indicators, the researchers do not have this knowledge from previous research, a pilot study may be carried out using a limited number of animals. This will aid in refinement by not allowing a large study to take place with no prior knowledge of humane endpoints that could cause further suffering. Researchers must also ensure that the humane endpoints that are decided on are reproducible, easy, and efficient to monitor, will not interfere with the procedures before necessary (potentially leading to more animals being used), and are relevant to both the animals and the procedures.  

Humane endpoint indicators 

There are many indicators that should be considered when determining humane endpoints. Indicators broadly fit into two categories: physiological and behavioural, and will be different depending on the species and procedures taking place.  

Physiological indicators can include increased/decreased respiration rate, change in blood count, weight loss, increased/decreased heart rate, and dehydration, as well as hormonal and biochemical changes. Clinical signs, such as tumour formation are also indicators that will be dependent on the type of research and procedures that the animal is a part of.  

Behavioural indicators can include a change in activity level, unusual posture, aggression, unusual response to handling and restraint, changes to grooming, vocalisation, changes to usual hunger and thirst.