FOOD SUPPLEMENTATION DURING LACTATION SHORTENS ANESTRUS AND ELEVATES GONADOTROPINS IN RATS

Breastfeeding delays the resumption of ovulation in women, a phenomeno n particularly important in less developed areas. Although human and a nimal studies indicate that undernutrition extends the period of lacta tional anestrus, the effect of improving nutritional status during lac tation on this time of infecundability, however, is less clear, To ass ess the effects of food supplementation on duration of lactational ane strus, Sprague-Dawley rats were assigned to one of three dietary group s: I) control (C), given unrestricted access to diet AIN-76A(TM);2) fo od-restricted (FR), fed 50% of the control intake; and 3) food-supplem ented (FS), food-restricted until d 0 of lactation and thereafter give n unrestricted access to diet AIN-76A(TM). Time to first detectable pr oestrus was monitored starting on d 10 of lactation. Nursing behaviors and gonadotropin and prolactin concentrations were measured in both i ntact and ovariectomized dams on d 10, 15 and 20 of lactation; we repo rt these data only on the ovariectomized group, which represents the m ore appropriate animal model of human reproductive physiology during l actation. 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 sti mulating hormone concentrations than FR rats (P < 0.0001 for each). Pr olactin concentrations were lower on d 20 than on d 10 of lactation fo r 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 experience d less suckling (P < 0.05) than FR rats on d 15 of lactation. These re sults indicate that food supplementation of previously underfed rats h astens the return of ovulation and is accompanied by alterations in nu rsing behaviors.