Environmental complexity in laboratory animal housing goes beyond meeting minimum space requirements, addressing cognitive and behavioural needs that directly affect welfare and scientific validity.
Laboratory animal housing that meets minimum regulatory standards may still fall well short of providing adequate welfare. Minimum space requirements ensure physical survival but not psychological wellbeing. Environmental complexity — nesting material, hiding structures, running wheels, gnawing objects, and social housing where species-appropriate — addresses the cognitive and behavioural needs that determine psychological welfare. Importantly, enrichment is not merely a welfare concern but a scientific quality issue: stressed, bored animals in impoverished environments show elevated baseline stress markers and greater variability in experimental responses, potentially confounding results. The scientific and welfare case for environmental complexity is therefore aligned rather than in tension. Embedding environmental complexity as a standard expectation rather than an optional addition would improve both outcomes simultaneously.