Environmental complexity in laboratory animal housing — including hiding places, nesting material, and social grouping — significantly improves welfare and in many cases also improves experimental reproducibility.
Laboratory animal housing has historically prioritized experimental control over animal welfare, based on the assumption that environmental complexity introduces confounding variables. Evidence now strongly challenges this assumption: animals in barren environments have elevated chronic stress that alters every physiological parameter researchers measure. Enriched animals actually produce more consistent and reproducible results because their baseline physiology is more stable. Nesting material for mice is one of the most striking examples — it costs almost nothing, dramatically reduces chronic stress, improves thermoregulation, and has been shown to affect experimental outcomes in ways that barren housing obscures. The welfare and scientific cases for housing complexity align rather than conflict.