Mice are intensely social animals, yet many research facilities house them individually — a practice with significant welfare costs that also affects research validity.
Individual housing of laboratory mice represents an unnecessary welfare cost in many cases, as compatible pairs or small groups can be successfully housed together with proper management. The fact that social isolation also compromises research validity — by introducing stress-related confounds — strengthens the case for change on both welfare and scientific grounds. Facilities transitioning to group housing report manageable levels of aggression when appropriate environmental complexity is provided. Institutional animal care committees should scrutinize individual housing justifications carefully and require evidence that group housing was genuinely attempted.