Mice and rats account for over 90% of all animals used in research. Their welfare is critically important given their numbers — yet they are among the least protected research animals legally.
Laboratory mice and rats experience welfare harms from housing conditions, experimental procedures, and the chronic stress of a highly controlled, abnormal environment. Standard mouse cages are typically too small for natural locomotion and social behaviour. Single housing — still common despite evidence for distress from social isolation — prevents natural grooming, sleeping-together, and play. Procedures including tumour implantation, wound creation, and toxin exposure cause significant acute and chronic pain. The Mouse Grimace Scale has improved detection and treatment of pain but adoption is not universal. Cage enrichment (nesting material, huts, running wheels) is now standard in many facilities but remains inconsistently applied.