Litter Size: A Latent Social Behavior Effect Exhibited by Charles River Rats

Abstract

Measures of open-field social behavior were devised and the results assessed as a function of pre-weaning rearing practices. Rat pups were raised in large (12 pups per mother) and small litters (6 pups per mother). An analysis of variance indicated sex effects during social interaction at 21 days of age. The female vs female pairs and the male vs female pairs, each exhibited a significantly greater social interaction score than the male vs male pairs although there were no significant differences between the female and mixed-pair groups. However, a latent litter effect was observed when the subjects were tested at sexual maturity, 64 days of age. The results indicated that subjects raised in larger litters exhibited a longer duration of body contact and a significantly higher social interaction score than those subjects reared in small litters. The investigators discuss the point that social behavior is of the utmost importance to sexually mature animals. Thus, the effects of previous rearing conditions may have been delayed until social behavior becomes a mechanism for enhancing the reproductive behavior of that species.