Group-housed male mice are highly prone to escalating aggression and injurious fighting, and routine full cage changes plus unfamiliar cage-mate pairings make it worse.

The hack / solution

Switch from a full weekly or fortnightly cage change to spot-cleaning only when needed — spot cleaning alone is associated with a lower prevalence of aggression than a full change. 2) When a full change can't be avoided, transfer some clean, dry nesting material into the new cage instead of washing away every scent cue with fresh bedding only. 3) Group littermates together before sexual maturity rather than mixing unfamiliar adult males later, since cage-mates selected from the same litter show less aggression. 4) Add cage partitions or extra tunnels to increase cage complexity so subordinate mice can break line of sight from a dominant animal — this reduced aggression specifically in BALB/c males in controlled testing. 5) Keep female scent away from all-male cages entirely; introducing female odor is a major, avoidable trigger for fighting.

📎Source: NC3Rs — Minimising Aggression in Group-Housed Male Mice🔗View source🗓️Added: 2026-07-16✅Reviewed by: MouseStuff Admin