Effect of progestogen plus estradiol-17beta treatment on superovulatory response in beef cattle

A series of 3 experiments were conducted to evaluate superovulatory response following exogenously controlled follicular wave emergence in cattle. In Experiment 1 the hypothesis was tested that treatments with progestogen plus estradiol-17beta (E-17beta) would result in the emergence of a wave of ovarian follicles that are as responsive to exogenous gonadotropins as those of a spontaneous follicular wave. Beef cows and heifers either received a progestogen ear implant on Day 0 (ovulation) plus 5 mg im E-17beta on Day 1 and were superstimulated on Day 5, or did not receive implants but were superstimulated on Day 8 (expected day of emergence of the second follicular wave). The cattle received 400 mg NIH-FSH-P1 of Folltropin-V, given in a single subcutaneous injection or twice daily as intramuscular injections over 4 d. No significant differences were detected between the 2 groups in the number of corpora lutea (CL), ova/embryos collected, fertilized ova and transferable embryos. In Experiment 2 superstimulatory responses to a single subcutaneous injection of Folltropin-V were compared between heifers in which follicle wave emergence was synchronized with progestogen plus E-17beta at unknown stages of the estrous cycle with those treated following a conventional method of superstimulation at middiestrus. Superstimulation 4 d after E-17beta treatment in heifers with progestogen implants resulted in a similar superovulatory response and higher fertilization rates than those initiated 8 to 12 d after estrus. In Experiment 3 the ovarian response to a single- versus multiple-injection superstimulatory treatment protocol was compared in heifers given progestogen plus E-17beta to induce synchronous wave emergence. The number of CL, ova/embryos collected, fertilized ova and viable embryos were not different between groups. Superstimulatory treatments initiated 4 d after E-17beta treatment of cattle with progestogen implants resulted in comparable ovulatory responses to treatments initiated at the time of spontaneous wave emergence or during middiestrus. Synchronizing wave emergence in a group of randomly cycling cattle obviated the need of estrus detection and synchronization prior to superstimulation.