Extreme inbreeding will compromise an animal's ability to discriminate between individuals and, thus, assess familiarity and kinship with conspecifics. In rodents, a large component of individual recognition is mediated through chemical communication. The counter-marking of competitor males' scent marks provides a measure of discrimination between their own scent and that from other individuals. We investigated whether males in common outbred (ICR(CD-1) and TO) and inbred (BALB/c) strains of laboratory mice could recognize the urinary scents of other individuals by measuring their investigation and counter-marking responses. Dominant males of outbred strains investigated and counter-marked scents from other males, whether of the same or another strain. Dominant inbred BALB/c males investigated but did not counter-mark their own strain scents, counter-marking only those from another strain. They did not use environmentally induced status differences in odours to recognize scents from other males. The inability of the inbred mice to discriminate between their own scent marks and those of other males is likely to alter their competitive behaviour, which could influence responses in experiments and the welfare of caged laboratory mice.
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