Research animal facilities are required to maintain suitable environmental conditions for housing different species. These are described in detail in the UK Home Office Code of Practice.
The temperature, relative humidity, lighting and noise levels in animal holding rooms should all be controlled so that they meet the physiological and ethological needs of the animals housed in the facility. Equally important is ensuring that these conditions are also maintained within animal cages. Rats and mice are social animals, so whenever possible they should be housed in stable social groups. Removing individual animals for euthanasia can disrupt these groups and lead to aggression. Planning studies carefully, and being alert to this problem, can help prevent serious injuries caused by fighting between cage mates.
Cages must provide suitable food, water and bedding, and be constructed of suitable materials. They must also provide sufficient space with sufficient complexity to allow animals to express their normal behaviour, and so far as is practicable, to fulfil their behavioural drives. Various environmental enrichment devices can be provided for rodents, for example, nesting materials, and tubes and containers. Even when animals are being housed for relatively short periods, prior to euthanasia, it is important that these provisions for improving their welfare are made.