Minimum space standards for laboratory animals in many countries are based on outdated research and fail to provide adequate room for normal behavior, contributing to chronic welfare deficits.
Laboratory animal housing standards represent a case where regulations have failed to keep pace with scientific understanding. Mice in minimum-size cages cannot perform several natural behaviors including running, foraging, and social avoidance. The chronic stress of inadequate space manifests as elevated corticosterone, immune suppression, and behavioral pathologies that affect research results as well as welfare. Updating standards to reflect current welfare science would benefit animals and improve research quality simultaneously. The economic barrier — larger cages mean fewer animals per room — is real but increasingly offset by the cost of irreproducible results from stressed animals.