Periovulatory LH, FSH and steroid hormone profiles in superovulated and unstimulated holstein heifers

Abstract

Periovulatory gonadotrophin and steroid hormone profiles were compared between superovulated and unstimulated Holstein heifers. Treatment was induced in luteal-phase heifers with 8 injections of FSH (superovulated n=9) or saline (unstimulated n=3) given over 5 d. Both groups received 0.5 mg of cloprostenol (PG) with the sixth injection of FSH or saline to induce luteolysis. All animals were inseminated at estrus, and embryos were collected at Day 7 of gestation. Blood samples were taken hourly for 6 h after the morning injection of FSH (or saline) and then every 15 min for 3 h (from 1400 to 1700 h) on each of the 5 treatment days. Before PG, mean serum progesterone and estradiol concentrations were higher (P ≤ 0.05) and LH pulse frequency and amplitude were lower (P ≤ 0.05) in the superovulated than the unstimulated heifers. After PG, mean serum progesterone and estradiol concentrations were higher (P ≤ 0.05), LH pulse frequency and amplitude (P ≤ 0.001), and basal serum LH concentration (P ≤ 0.05) were lower in the superovulated than in the unstimulated heifers. After PG injection, the superovulated heifers had reduced FSH pulse amplitude compared with that before the injection (P ≤ 0.05). In the superovulated cows, the suppression of LH and FSH secretion was caused by the negative effects of higher concentrations of estradiol and progesterone in the hypothalamic-hypophysal axis. In the superovulated heifers, 30 h after PG treatment, serum estradiol concentration and LH pulse frequency were positively correlated with the number of CL, total number of embryos, and transferable number of embryos recovered (P ≤ 0.05).