This study was conducted to compare efficacy of treatments with EB or GnRH and different quantities of exogenous progesterone (P₄) for synchronization of time of ovulation on follicular growth and pregnancy in lactating dairy cows. In Experiment 1, 40 cows were treated with EB or GnRH and 1.9 or 3.0 g of P₄ via progesterone-containing intravaginal devices (IVPD; D0), two doses of PGF_2α on D7, GnRH on D9, and TAI on D10. In Experiment 2, 1,440 cows were treated with EB or GnRH and 1 g IVPD on D0, cloprostenol, eCG and EB on D7. Cows in estrus by 48 h were AIDE, and non-estrous cows were administered GnRH and TAI 60 h after IVPD removal. Non-estrous cows were AIDE 72 h after IVPD removal. In Experiment 1, P₄ was greater on D7 for cows treated with GnRH than those treated with EB. The dominant follicle was larger for cows treated with GnRH than those treated with EB. In Experiment 2, for estrous cows, pregnancy per AI was greater in cows AI at 48 h compared to 60 h after IVPD removal for cows treated with GnRH, and greater with AI at 60 h after IVPD removal compared to 48 h in EB-treated cows. In non-estrous cows, there was no effect on pregnancy. In conclusion, treatment with GnRH compared with EB resulted in increased P₄ regardless of amount of exogenous P₄, and there were differential proportions of estrous cows pregnant depending on time of AI after IVPD removal.

本研究旨在比较 EB 或 GnRH 和不同量的外源性孕酮 (P ₄ ) 处理同步排卵时间对泌乳奶牛卵泡生长和妊娠的疗效。在实验 1 中，40 头奶牛通过含孕酮的阴道内装置（IVPD；D0）用 EB 或 GnRH 和 1.9 或 3.0 g P ₄治疗，第 7天注射两剂 PGF _2α，第 9 天注射GnRH ，第 10 天注射TAI。在实验 2 中，1,440 头奶牛在第 0 天接受了 EB 或 GnRH 和 1 g IVPD，在第 7 天接受了氯前列醇、eCG 和 EB。48 小时前发情的奶牛是 AIDE，非发情奶牛在去除 IVPD 后 60 小时接受 GnRH 和 TAI。非发情奶牛在 IVPD 去除后 72 小时进行 AIDE。在实验 1 中，P ₄用 GnRH 治疗的奶牛在第 7 天比用 EB 治疗的奶牛更大。用 GnRH 处理的奶牛的优势卵泡比用 EB 处理的那些大。在实验 2 中，对于发情的奶牛，与使用 GnRH 治疗的母牛去除 IVPD 后 60 小时相比，AI 在 48 小时的每 AI 妊娠率更高，而在去除 IVPD 后 60 小时的 AI 与 EB 治疗的 48 小时相比更高奶牛。在非发情奶牛中，对妊娠没有影响。总之，与 EB 相比，GnRH 治疗导致 P ₄增加，而不管外源 P ₄的量如何，并且根据去除 IVPD 后 AI 的时间，发情母牛怀孕的比例不同。