Mice are the most commonly used laboratory animals, and improving their welfare is essential given that millions are used in research annually.
Laboratory mice have complex social and cognitive needs that standard laboratory housing often fails to meet. Isolation causes significant psychological distress in these highly social animals. Environmental enrichment, including nesting material and hiding spaces, dramatically improves welfare with minimal impact on research validity. The refinement principle of the 3Rs framework calls for minimizing suffering, but implementation varies widely. Given the enormous numbers used, even small welfare improvements have massive aggregate impact.