Periovulatory LH, FSH, and steroid hormone profiles in superovulated and unstimulated Holstein heifers
1995
Roberge, S. | Rieger, D. | Rawlings, N.C.
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 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 less than or equal to 0.05) and LH pulse frequency; amplitude were lower (P less than or equal to 0.05) in the superovulated than the unstimulated heifers. After 1 mean serum progesterone and estradiol concentrations were higher (P less than or equal to 0.05), LH pulse frequency and amplitude (P less than or equal to 0.001), and basal serum LH concentration (P less than or equal to 0.05) were lower in superovulated than in the unstimulated heifers. After PG injection, the superovulated heifers had reduced FSH pulse amplitude compared with that before the injection (P less than or equal to 0.05). In 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 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,; transferable number of embryos recovered (P less than or equal to 0.05).
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