Food supplementation during lactation shortens anestrus and elevates gonadotropins in rats

Breastfeeding delays the resumption of ovulation in women, a phenomenon particularly important in less developed areas. Although human and animal studies indicate that undernutrition extends the period of lactational anestrus, the effect of improving nutritional status during lactation on this time of infecundability, however, is less clear. To assess the effects of food supplementation on duration of lactational anestrus, Sprague-Dawley rats were assigned to one of three dietary groups: 1) control (C), given unrestricted access to diet AIN-76A; 2) food-restricted (FR), fed 50% of the control intake; and 3) food-supplemented (FS), food-restricted until d 0 of lactation and thereafter given unrestricted access to diet AIN-76A. Time to first detectable proestrus was monitored starting on d 10 of lactation. Nursing behaviors and gonadotropin and prolactin concentrations were measured in both intact and ovariectomized dams on d 10, 15 and 20 of lactation; we report these data only on the ovariectomized group, which represents the more appropriate animal model of human reproductive physiology during lactation. Proestrus returned significantly (P < 0.0001) sooner in both FS (18.1 +/- 2.4 d) and C (18.0 +/- 2.9 d) than in FR (28.8 +/- 2.8 d) intact dams. FS rats had higher luteinizing hormone and follicle stimulating hormone concentrations than FR rats (P < 0.0001 for each). Prolactin concentrations were lower on d 20 than on d 10 of lactation for all groups (P < 0.02), but we found no effect of dietary treatment. FS rats spent more time away from their pups (P < 0.05) and experienced less suckling (P < 0.05) than FR rats on d 15 of lactation. These results indicate that food supplementation of previously underfed rats hastens the return of ovulation and is accompanied by alterations in nursing behaviors.