The effects of rearing environment on pup development.

Norway rats were reared either in a standard laboratory cage or in a nest constructed by the dam from newspaper strips. Growth, thermoregulatory ability, and adrenal, gonad, adipose tissue, and brain weights were measured at weaning on Day 21 postpartum. While there was no difference in growth, nest-reared animals had lower body temperatures, but could thermoregulate as well as cage-reared animals. Nest-reared animals also had relatively smaller adrenals and less brown adipose tissue. Gonad and brain weights were similar. An interesting finding was that males and females were differentially affected by the nest-rearing. Differences between cage- and nest-reared animals were more evident in females, and thermoregulatory ability was more closely associated with the quality of the nest during the first 10 days than body weight in females. For males, body weight was more important. These latter data are discussed in relation to differential interaction between the dam and male and female pups.