Laboratory mice are the most commonly used research animals globally. Evidence consistently shows that group housing and environmental enrichment improve welfare and reduce experimental variability, benefiting both animals and science.
Laboratory mouse welfare has improved substantially through application of evidence from behavioral science. The recognition that isolated housing causes chronic stress - and that this stress affects experimental outcomes - created alignment between welfare and scientific validity. Stressed mice are different from unstressed mice at biochemical, behavioral, and physiological levels that matter for research reproducibility. Enrichment provision is now a welfare requirement in most jurisdictions and is increasingly seen as essential for producing valid, reproducible research. The remaining welfare challenges include single housing justified by experimental design when alternatives exist, failure to provide adequate nesting material due to cost or convenience, and thermal environments at the low end of mouse thermoneutrality.