Mice are the most widely used laboratory animals, with over 100 million used annually worldwide. Simple refinements to housing and husbandry can dramatically improve their welfare without compromising scientific validity.
Mouse welfare in laboratories has historically been undervalued relative to larger species, partly because mice are small and their distress expressions are subtle. Yet the scale of mouse use makes welfare improvements exceptionally impactful across the global research system. Tail handling causes measurable fear and pain — switching to tunnel or cup handling is free, takes no additional time, and reduces stress hormones that can confound experimental results. Providing nesting material costs pennies per cage and substantially reduces stereotypic behaviors and cold exposure. Social housing of compatible mice reduces chronic stress and is now standard in most guidelines. These refinements align welfare improvement with better science — stressed mice produce more variable data, reducing experimental reliability.