Mice and rats used in biomedical research are typically housed in barren cages, despite strong evidence that enrichment improves both welfare and experimental reliability.
Laboratory rodents kept in barren cages show elevated stress hormones, abnormal repetitive behaviours, and reduced immune function — all of which affect the quality and generalisability of research findings. The Three Rs principle of Refinement requires that housing be improved to reduce suffering. Despite this, barren caging remains common, partly due to concerns about standardisation. Evidence shows that enriched housing can be standardised and that variability introduced by enrichment is smaller than variability from stress-induced physiological changes in impoverished animals. Welfare improvement and scientific quality reinforce each other.