Mice and rats used in biomedical research show improved welfare and research validity when provided with appropriate environmental enrichment; barren cages are both unnecessary and counterproductive.
Laboratory rodents in barren cages experience chronic frustration of nesting, burrowing, and social behaviours. Paradoxically, the welfare improvements associated with enriched environments also improve research reproducibility by reducing stress-induced physiological variation. The misconception that welfare improvements confound research outcomes has been challenged by evidence showing enrichment reduces rather than increases outcome variability.