Laboratory Mouse Enrichment: From Bare Cages to Species-Appropriate Housing

Mice are the most commonly used laboratory animals globally. Enrichment programmes that address their burrowing, nesting, and social needs improve welfare and research validity simultaneously.

Key Facts

Approximately 100–115 million mice are used in scientific research globally each year, representing 60–80% of all laboratory vertebrates.
Standard laboratory mouse caging — small, transparent plastic boxes — provides little opportunity for species-typical behaviours like burrowing, nesting, and hiding.
Mice in enriched cages (with nesting material, shelters, and running wheels) show lower corticosterone levels, reduced aggression, and higher cognitive test performance.
Nesting material is one of the highest-priority enrichments for mice: it satisfies thermoregulatory needs and is consistently chosen when available.
Running wheels address high voluntary activity needs; mice in laboratory settings are much less active than wild counterparts, leading to metabolic differences that can confound research.
Group housing is essential for social species like mice; single housing causes chronic stress that alters immune function, pain sensitivity, and behaviour.

Welfare Considerations

Bare cage housing for laboratory mice fails to meet even basic behavioural needs. Wild mice build complex burrow systems, construct elaborate nests, run several kilometres nightly, and live in social groups. Stripping these opportunities away causes measurable chronic stress — elevated glucocorticoids, reduced immune function, stereotypic behaviours, and abnormal aggression. Beyond the ethical problem, stressed mice with altered physiology produce research data that translates poorly to human medicine. Enrichment is therefore both an ethical obligation under the 3Rs framework and a scientific necessity. Resistance from some researchers who worry enrichment introduces variability is increasingly countered by evidence that enriched animals show more consistent, replicable baseline measures.

What You Can Do

Support the NC3Rs and similar organisations that fund and promote laboratory animal enrichment research.
Advocate for institutional animal care committees (IACUCs) to require nesting material, shelters, and social housing as defaults.
Support training programmes for laboratory animal technicians that include enrichment implementation skills.
Follow and share research demonstrating that enrichment improves both welfare and research quality.
Engage with research institutions to ask about their enrichment policies for commonly used species.