Mice are by far the most commonly used research animals, with over 100 million used annually worldwide, yet their welfare receives less public attention than larger animals.
Laboratory mice in standard caging experience significant welfare deprivation. Smooth-bottomed polycarbonate cages provide no burrowing substrate, minimal nesting material, no hiding places, and no running opportunities. Mice in barren caging show chronic mild stress that affects behavior, physiology, and research outcomes. Ironically, welfare improvements may also improve research quality by reducing stress-induced variability. The 3Rs framework requires refinement of housing and procedures. Provision of nesting material, which is inexpensive and simple, is among the most beneficial welfare improvements demonstrating responsiveness to one of mice highest-priority behaviors. Carbon dioxide euthanasia, standard in many labs, causes pain before unconsciousness and superior alternatives exist. Social housing is essential as mice are highly social.