EFFECTS OF ENERGY-SOURCE IN THE DIET ON REPRODUCTIVE HORMONES AND INSULIN DURING LACTATION AND SUBSEQUENT ESTRUS IN MULTIPAROUS SOWS

Two experiments were performed. The first experiment was done to study the effects of dietary energy source on plasma insulin concentration using five gilts in a Latin square design with two diets over two peri ods. The diets contained either 200 g/kg of cornstarch (Starch) or soy bean oil (Fat) as energy sources. Results indicate that insulin respon se was greater in the Starch-fed than in the Fat-fed gilts. A second e xperiment was performed in which 18 multiparous sows were fed one of t he two experimental diets from farrowing until slaughter at d 35 of su bsequent pregnancy. All sows nursed nine pigs. Blood samples were take n from a permanent jugular vein catheter every 12 min during a 12-h pe riod on d 109 +/- 1 of pregnancy, on d 7 +/- 1, 14 +/- 1, and 21 +/- 1 of lactation, and on the day of weaning (d 22 +/- 1). From 48 h after weaning, blood samples were taken every 4 h until 24 h after ovulatio n. After that, blood samples were taken at 12-h intervals until d 10 a fter ovulation. Differences between diets in insulin response were not significant. In Starch-fed sows, LH pulsatility at d 7 of lactation w as greater (P < .05), the preovulatory LH surge was greater (P < .05), and progesterone production was greater (P < .05) from 108 h until 25 6 h after the LH surge than in the Fat-fed sows. Results indicate that feeding Starch-rich diets to multiparous sows compared with Fat-rich diets, on an isocaloric basis, increases LH pulsatility during early l actation, the preovulatory LH surge, and progesterone production after the LH surge.