Mice are by far the most commonly used laboratory animals, with tens of millions used annually. The 3Rs framework (Replace, Reduce, Refine) guides welfare improvement, but implementation varies widely across institutions.
Laboratory mouse welfare is affected by both experimental procedures and the housing conditions in which mice live between procedures. Social isolation — common in many research protocols — causes chronic stress that affects behaviour, physiology, and experimental results, creating a welfare problem that also compromises scientific validity. Handling stress, injection procedures, and tissue collection cause acute welfare harm that can be reduced through refined techniques and trained staff. Pain management in experimental models is inconsistently applied — many pain models provide no analgesia because researchers fear confounding results, creating significant welfare harms that are ethically questionable. Enriched housing with nesting material, group housing, and environmental complexity can substantially improve welfare with minimal experimental impact, yet adoption remains incomplete across global research institutions.