Laboratory animal facilities have been designed to provide a standard environment where animals can be kept in good physical health at the same time as economic and ergonomic considerations are met. Recognizing the potential welfare problem associated with behavioural restriction in such housing systems, a number of attempts have been made to improve this environment, generally described under the term 'environmental enrichment'. Modifications of cages for mice usually consist of providing material for nest building and structures which can serve as hiding places and/or for climbing. We have reviewed 40 studies carried out between 1987 and 2000, in which preferences as well as the effect of housing modifications have been studied. Mice will work for access to nesting material and make use of this material to make nests in which they rest. They prefer a more complex cage to the standard cage and will also work for access to cages with shelter and raised platforms. On the basis of present knowledge, it is recommended that mice should have access to nesting material. Strategies for future research are outlined in the article.

In 1986, European Directive 86/609/EEC, regulating the use of animals in research, was one of the first examples of common legislation to set standards for animal protection across the Member States of the former European Economic Community, now the European Union, with the aim of securing a level European playing field. Starting in 2002, a process of revising European animal experimentation legislation was undertaken, with one of its key aims being to ensure high standards of welfare for laboratory animals across Europe. This resulted in Directive 2010/63/EU, which has regulated this activity in Europe since 2013. Since this is a European Union Directive, transposition into national legislation is a necessary and important part of the implementation of the new legislation. This paper gives an overview of the transposition process followed by an analysis of the potential to reach the different objectives of the directive, particularly with a focus on securing the same high standards of animal protection across member countries. The analysis focuses on three separate issues: (1) minimum standards for laboratory animal housing and care, (2) restrictions on the use of certain animal species, and (3) project review and authorization.