Laboratory Mouse Welfare: Refinement in the Most Used Research Animal

Mice are the most widely used research animals globally, and significant advances in welfare refinement over the past decade are improving their lives while maintaining or improving scientific outcomes.

Key Facts

Approximately 100 million mice are used in research worldwide annually, accounting for over 60% of all laboratory animal use.
Standard laboratory caging has historically provided minimal environmental complexity — wire mesh floors, no nesting material, and social isolation — that is increasingly recognized as causing chronic stress.
Providing nesting material to laboratory mice reduces stress hormones, improves immune function, and produces more reproducible experimental results.
The "grimace scale" for mice — a validated facial action coding system — allows researchers to assess pain levels non-invasively and adjust analgesia accordingly.
Standard laboratory mice housed under white light 12-hour cycles show disrupted circadian rhythms that affect behavior, metabolism, and experimental results.
Tail-vein injection, the most common route of drug administration in mice, causes significant distress — training mice to accept injections voluntarily reduces stress for both animals and researchers.

Welfare Considerations

The paradox of laboratory mouse welfare is that many standard practices that compromise welfare also compromise science: stressed animals have dysregulated physiology that reduces reproducibility and introduces experimental confounds. The business case for refinement therefore aligns with the welfare case in ways that make improvement more achievable than in other animal use contexts. Provision of nesting material costs cents per mouse per week and demonstrably improves both welfare and data quality. Grimace scale assessment enables real-time pain management decisions. Voluntary participation training reduces stress during procedures. These refinements have moved from experimental novelty to recommended practice in a decade, driven by the convergence of welfare and scientific evidence. The challenge now is implementing them consistently across institutions.

What You Can Do

Support the NC3Rs (National Centre for the Replacement, Refinement and Reduction of Animals in Research) programs that develop and disseminate welfare refinements.
Advocate for institutional animal care and use committees (IACUCs) to require justification for departing from enriched housing standards.
Support funding for research into non-animal alternatives that could eventually reduce mouse use.
Encourage transparency in laboratory animal welfare reporting through support for open science policies.
Engage with your institution's research ethics board to advocate for adoption of current best-practice refinement standards.