Mice are the most commonly used laboratory animals, with tens of millions used annually worldwide. Refinement — improving conditions and reducing suffering — is the most immediately achievable 3Rs goal.
Mice in conventional laboratory housing experience significant welfare deficits from barren environments, social isolation, and the stress of experimental procedures. As social animals, individually housed mice show elevated stress hormones and abnormal behaviour. Barren cages prevent natural behaviours including nesting, burrowing, and exploration. The development of validated pain assessment tools like the Mouse Grimace Scale has enabled better pain management by providing objective measures. Refinement — social housing, environmental enrichment, validated anaesthesia and analgesia protocols — improves both welfare and research data quality by reducing stress confounds.