Effects of different patterns of feed restriction and insulin treatment during the luteal phase on reproductive, metabolic, and endocrine parameters in cyclic gilts.

The objectives of the present study were 1) to study potential effects of previous nutritional treatment on developmental competence of early fertilized oocytes in vitro; 2) to study responses to insulin treatment during the period of feed restriction in the late luteal phase which has deleterious effects on subsequent fertility; and 3) to establish the metabolic and endocrine status of gilts during treatment and the subsequent periestrous period. Nineteen trios of littermate gilts were subjected to feed restriction during the first (RH) or second (HR) week of the estrous cycle. A second group of HR gilts received injections of long-acting insulin during their period of feed restriction (HR+I). Intensive sampling was performed in a subgroup of 23 animals on d 15 and 16 of the cycle for analyses of endocrine (gonadotropins and steroid hormones) and metabolic (insulin, IGF-I, leptin, total triiodothyronine [T3], and free T3) variables. Gilts were checked for estrus every 6 h, and time of ovulation was monitored by transcutaneous ultrasonography. Surgeries were performed 12 to 20 h after ovulation, and the early-fertilized oocytes recovered were cultured in vitro under standardized conditions. There was no treatment effect on the developmental competence of fertilized oocytes in vitro; however, ovulation rate was increased in HR+I gilts. No effect of treatment was observed on plasma leptin and IGF-I concentrations on d 15 and 16. However, HR+I gilts had higher (P < 0.05) postprandial insulin and lower (P < 0.05) postprandial total and free T3 on d 15. Plasma concentrations of LH, FSH, and progesterone on d 15 and 16 and plasma estradiol concentrations on d 16 were not affected by previous nutritional or insulin treatment. In the periestrous period, plasma concentrations of LH, FSH, and estradiol were higher (P < 0.05) in RH and HR+I, and the rise in plasma progesterone after the LH surge was lower (P < 0.05), than in HR gilts. No effect of treatment was observed on plasma concentrations of metabolic hormones, except on plasma leptin concentrations, which were higher (P < 0.05) at the time of the LH surge in RH gilts. These results suggest that feed restriction during the late luteal phase may have deleterious effects on ovarian function in the periestrous period, which may be counteracted by insulin.