These systems provide adequate, basic physiological requirements of animals, but only marginally fulfil other needs, such as the performance of natural behaviour or social interactions.
Many signs indicate that the current housing conditions affect the well-being of animals negatively.
Environmental enrichment may solve some of the problems caused by the restrictive laboratory environments, because the more structured environment allows the animals to perform species-specific behaviour. When introducing enrichment it is important to evaluate the effects of the enrichment programme used. In the first study described in this thesis, the effects of relatively simple environmental enrichment provided in standard laboratory cages on the behaviour of mice in three behavioural tests were investigated. Effects of enrichment on the behaviour of the mice were found, although the effects differed per strain. Choice tests have been used to assess laboratory animals' preferences for different environments or for aspects of the environment.