Effect of estradiol benzoate or GnRH treatment prior to superstimulation in CIDR-treated, Korean native cows (Bos taurus)

The objective of this study was to evaluate the effectiveness of superovulatory protocols by synchronizing the emergence of the follicular wave using estradiol benzoate (EB) or GnRH in CIDR-treated, Korean cows. Sixty-six cows were used in the study and these were divided into three groups. The standard group comprised cows that were between days 8 and 12 of their estrous cycle (n = 22). The remaining 44 cows, at all other stages of the estrous cycle, received CIDR and were assigned to two treatment groups that received either 2 mg EB (EB-CIDR group, n = 22) or 100 μg GnRH (GnRH-CIDR group, n = 22) 1 day after CIDR insertion. Gonadotropin treatment began between the 8th and 12th days of the estrous cycle in the standard group, 5 days after EB injection in the EB-CIDR group, and 3 days after GnRH injection in the GnRH-CIDR group. All cows were superovulated with porcine FSH (pFSH) twice daily, with the dose (total 28 mg) decreasing gradually over 4 days. On the 5th and 6th injections of pFSH, 25 and 15 mg doses of PGF2α were administered. CIDR was withdrawn at the 7th pFSH injection and the cows received 200 μg GnRH at 24 h after CIDR withdrawal. Cows were artificially inseminated twice at 36 and 48 h post-CIDR withdrawal and embryos were recovered 7 days after the 1st insemination. The numbers of preovulatory follicles (22.9-28.2), ovulated preovulatory follicles (17.6-21.7) and CL (15.9-17.9) detected by ultrasonography did not differ among groups (P > 0.05). Similarly, the numbers of total ova (6.7-10.0), transferable embryos (4.0-6.0), degenerate embryos (1.1-1.8) and unfertilized ova (1.3-4.3) did not differ among groups (P > 0.05). Progesterone and estradiol concentrations during superovulation treatments and at embryo recovery were also the same in all groups (P > 0.05). We conclude that in CIDR-treated Korean native cows, superovulatory treatments that follow administration of either EB or GnRH (at any stage of the estrous cycle) result in both a superovulatory response and embryo yield comparable to conventional superovulation protocols.