Laboratory mice are the most widely used research animals globally, making their welfare improvements high-impact even when per-animal benefits are modest.
Laboratory mouse welfare improvement has unique leverage because the scale of use means small per-animal welfare improvements aggregate to enormous total welfare benefit. Nesting material provision, shown to improve welfare significantly, costs pennies per mouse. Group housing that meets social needs reduces chronic isolation stress for hundreds of millions of animals annually. The reproducibility argument for enrichment - that stressed, impoverished mice produce more variable experimental results - aligns commercial and welfare interests unusually well, making welfare improvement both ethical and scientifically rational in research settings.