Mice and rats constitute over 90% of research animals globally, and their welfare is shaped by housing conditions, enrichment, and experimental endpoints.
Laboratory rodent welfare has improved substantially over the past 20 years, driven by research demonstrating that enriched housing produces both better animal welfare and more translationally valid science. Stressed, unhealthy animals produce more variable results, undermining the scientific value of their use. Nesting material, shelter structures, and foraging enrichment are now recognized as minimum standards in many institutional guidelines. The remaining welfare gaps are in endpoint recognition — many studies continue past the point where distress levels justify termination — and in housing conditions for male mice, whose aggression in group housing creates welfare challenges. The scientific and welfare case for continued improvement are aligned.