Group-housed male CD-1 mice show high levels of intermale aggression under a baseline wheel-plus-igloo-plus-tunnel enrichment setup, with injuries ranging from minor wounds to severe damage, and isolating them to stop the fighting just trades one welfare problem for another.

The hack / solution

Switch the baseline enrichment for one that keeps nesting material in the cage instead of relying on a wheel, igloo, and tunnel alone. 2) Add nesting material either alongside the existing wheel/igloo/tunnel setup or in place of the wheel and igloo (tunnel plus nesting) — both combinations cut fight-wound counts sharply versus the wheel/igloo/tunnel-only baseline. 3) In the study this was based on, baseline cages logged 77 fight wounds, while the nesting-enriched conditions logged only six to seven — a difference large enough to be worth testing in any high-aggression CD-1 colony. 4) Treat shredding opportunity, not just enrichment quantity, as the key variable: nesting material that can be shredded appears to redirect aggressive behavior in this outbred strain.

📎Source: PMC — A customised combination of environmental enrichment reduces aggression in CD-1 male mice🔗View source🗓️Added: 2026-07-16✅Reviewed by: MouseStuff Admin

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