Laboratory mice are the most commonly used research animals globally, and evidence-based enrichment significantly improves their welfare without compromising experimental validity.
Barren laboratory housing causes chronic stress in mice evidenced by elevated stress hormones, stereotypic wire gnawing, and abnormal behaviors. Mice in enriched environments show lower stress, better immune function, and more normal behavior. Early concerns that enrichment would increase variability in experimental outcomes have been largely disproven and some studies suggest enriched animals actually show more reproducible results reflecting less variation from chronic stress. The ethical obligation to improve mouse welfare is clear and the practical barriers are largely institutional inertia rather than genuine experimental necessity.