Mouse

Possibly 100 million years of evolution separate mice and humans but nevertheless some 99% of their genetic sequence is shared.

They can suffer from the same diseases such as diabetes, deafness and cancer. Mice are by far the most common research animal used in the UK - 63% of the procedures started in 2002 were with mice. As all mammals share so much in common, it makes sense for researchers to choose mice for their animal work if they can. Mice breed rapidly, have relatively short lives, and are cheap to buy and look after.

Despite the fact it will have been specially bred for research, the laboratory mouse behaves in a way shaped by its wild ancestry. It is largely nocturnal, likes the company of other mice and prefers to stay close to safe cover. Since rats are a mouse's natural predator, the two species are kept in different rooms. The short life expectancy in the wild is what encouraged mice to reproduce and develop fast, with large litters to maximise the chance that some offspring might survive.

The number of mice used in research is growing as more transgenics are bred. These have a change to their genes to make them more useful for research. Transgenic mice together with mice that have natural gene defects accounted for over half the total mice procedures in 2002.

Red appears dark to mice, so technicians can carry out checks when they are inside this shelter without disturbing them.

The large number of strains of mice is one of the challenges for their welfare. For example, in some strains, females attack other females or defend their nests vigorously against stronger males. As a result, group housing needs care. So, while hard and fast rules of husbandry for all types of mouse are not possible, general mouse needs have been identified. They are: bedding and nesting material (combination of two materials preferred), complexity in their cages, refuges and raised platforms, and chews.

As with all animals it is important not to assume what is best for the mouse. Mice do not rely on sight anywhere near as much as on smell. Animal technicians balance hygiene and maintaining the environment the way mice prefer. Over-zealous cage cleaning could disturb scent marking by the mice. Mice also have acute hearing - at ultrasound as well as human ranges - they do not like loud, unpredictable noises. So technicians try to keep the levels down around mice.

Mice particularly do not like bright lighting, so some laboratories use dim red lights to handle mice during the dark phase when they are active.

Some 40 different common activities and postures have been identified for mice. Their cages can be enriched by tubes, shelters, toys and so on to help them undertake as many of these activities as possible. Baffles and barriers are valuable too. They appear to reinforce the divisions mice make naturally - and scent mark - for different sorts of activity.