Effect of postnatal litter size on adult aggression in the laboratory mouse.

Growth, emotionality, food competition, and aggression were examined in mice nursed in litters of 3 or 9 and reared in isolation until testing. Animals from large litters were lighter at weaning and in adulthood and were more emotional in the open field than subjects from small litters. They did not win more food competition tests than subjects from small litters although their consummatory behavior during food competition tests was greater. Subjects from large litters were more aggressive in initial encounters, but over repeated encounters became more submissive. In a 2nd open-field test, emotionality of large-litter subjects was reduced more than that of subjects from small litters. When later placed in group-living cages, subjects from small litters sustained less long term physical assault than subjects from large litters. High correlations were found between the 4 measures of brief aggression.