Mice are by far the most commonly used vertebrate in biomedical research, accounting for approximately 60-70% of all laboratory animals. Their welfare is fundamental to both ethical research practice and the scientific reliability of results.
Mouse welfare science has advanced dramatically in the past two decades, revealing that standard research housing — small, barren cages with minimal enrichment — is inadequate for psychological welfare. Mice are cognitively active, social animals that spend a significant proportion of waking time foraging, playing, and exploring in naturalistic conditions. Barren housing produces chronically stressed animals with altered baseline physiology — a confounding variable that undermines experimental reproducibility. Providing nesting material, shelter, and running wheels improves welfare indicators without compromising experimental results and in many cases reduces inter-individual variation in measurements. The welfare and scientific quality arguments are aligned: better mouse welfare produces better science. The key challenge is ensuring that refinement practices are consistently applied rather than left to individual researcher discretion.