The contribution of changes in milk delivery to the prolongation of lactational infertility induced by food restriction or increased litter size

In rats, the length of lactational anovulation is prolonged when litter si; le is increased or when the dam is food restricted. In both of these situat ions the energetic demand on the dam is increased, milk delivery to each pu p is reduced, and consequently, patterns of pup suckling may be changed. We investigated the contribution of these factors to the maintenance of lacta tional anovulation by examining the effect of eliminating milk delivery on the length of lactational diestrus in food restricted and ad lib-fed female s nursing litters of 8 pups and in females nursing large (14 pups) and smal l (6 pups) litters. The results of these studies show that preventing milk delivery neither extends the period of lactational infertility in ad lib-fe d females nursing eight pups nor eliminates the effects of increasing litte r size on this period. (C) 1999 Elsevier Science Inc.