Mice and rats are the most commonly used laboratory animals globally; advances in refinement reduce suffering without compromising scientific validity.
Rodents have historically occupied a welfare middle ground in laboratory animal ethics — widely used, with established legal protections in most jurisdictions, but with refinement advancing unevenly across institutions. Pain assessment using validated grimace scales has transformed understanding of what procedures cause significant suffering, identifying conditions that were previously assumed to be minor welfare concerns. Refinement advances — tunnel handling, voluntary entry procedures, social housing, environmental enrichment, and appropriate analgesia — deliver substantial welfare improvements without compromising scientific outcomes and in some cases improve experimental reproducibility by reducing stress confounders. Embedding refinement as an ongoing priority rather than a one-time compliance exercise requires institutional culture change and veterinary leadership.