Food restricting lactating rat dams over the first 2 weeks of lactation results in a prolongation of the period of lactational diestrus. Such food restriction has not only a direct effect on the dam but also the pups are undernourished, and the pattern of dam-litter contact is also changed. In a series of studies, we investigated the effects of nursing undernourished pups and the change in dam-litter interaction on the prolongation of lactational diestrus. While nursing undernourished pups in the last 2 weeks of lactation is sufficient to extend lactational diestrus in ad Iib-fed dams nursing well-nourished pups in the last 2 weeks of lactation is not necessary for the prolongation of lactational diestrus seen in food-restricted dams. Further, neither nursing underfed pups nor increased nest time in the first 2 weeks postpartum are necessary factors for the prolongation of lactational diestrus in food-restricted dams. (C) 1995 Academic Press, Inc.
