Laboratory mice are by far the most used species in biomedical research. Housing standard improvements have significant welfare impact given the enormous numbers involved globally.
Mouse welfare improvements matter enormously in aggregate. Standard shoebox cages allow only minimal movement and no expression of natural burrowing, foraging, or climbing behavior. Isolation housing for adult mice causes anxiety-like states measurable through behavioral and physiological indicators. Providing nesting material alone has been shown to be the single most cost-effective enrichment intervention, improving reproductive success and reducing stress. Individually ventilated cage (IVC) systems improve air quality but can increase noise and vibration stress. Welfare assessment methods for mice have improved dramatically, enabling better pain recognition and earlier endpoint decisions. The 3Rs framework continues to drive meaningful improvements.