The effects of litter size and post‐weaning isolation or grouping on adult emotionality in C3H mice

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Abstract
Eighty‐three C3H mice were reared in litters of 2 or 8 pups until weaning and, thereafter, in isolation or in bisexual groups of 8‐10 animals in a Litter Size × Postweaning Experience × Sex factorial design. At 70‐75 days of age, subjects were tested in a modified version of the open‐field test, designed to overcome some of the reported difficulties in using the conventional test with mice. Animals reared in small litters obtained significantly higher scores than animals reared in large litters on 3 measures of exploratory behavior, though no differences were observed in defecation, eating, and grooming in the arena. Subjects isolated after weaning showed significantly more exploratory behavior and significantly less grooming, eating, and defecation in the test situation than animals kept in groups; males obtained significantly lower scores on 2 of the measures of exploratory behavior and on grooming than females. In general, the pattern of behavior shown by animals reared in larger litters, by animals grouped at weaning, and by males, is taken as indicating a higher level of emotionality.