Liu Tsung-Ching, Chiang Chen-Fei, Ho Chia-Tang, Chan Jacky Peng-Wen
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 40227, Taiwan.
Department of Veterinary Medicine, College of Veterinary Medicine, National Chung Hsing University, Taichung 40227, Taiwan.
Theriogenology. 2018 Jan 1;105:45-50. doi: 10.1016/j.theriogenology.2017.09.013. Epub 2017 Sep 9.
This study investigated the effect of gonadotropin-releasing hormone (GnRH) on ovulatory response after complete luteolysis induced by two low doses of prostaglandin (PG)F2α in lactating dairy cows. Cows (n = 18) ranging between 45 and 65 days in milk were recruited for synchronization by a modified Ovsynch-48 protocol (GnRH-7 days-375 μg PGF2α-1 day-250 μg of PGF2α-1 day-GnRH) over a total of 23 estrous cycles. Synchronized cows (n = 16) were randomly assigned to GnRH and Saline groups in stage 1 of the experiment after 9-10 days of ovulation in synchronization. On days 0 and 1 (day 0 = first PGF2α administration), cows were treated with 375 and 250 μg PGF2α, respectively. On day 2, cows in the GnRH and Saline groups were administered 250 μg GnRH or 2.5 mL of 0.9% saline, respectively. Serum progesterone (P4) levels were measured and changes in the corpus luteum (CL) were ultrasonically monitored daily from day 0-3 to assess complete luteolysis. Preovulatory follicle diameter and ovulatory response were evaluated by ultrasonography. In stage 2, cows were treated in a manner converse to that in stage 1. The synchronization rate was 69.6% (16/23). In stages 1 and 2, cows showed complete luteolysis with P4 concentration <1 ng/mL or remaining CL area <50%. Average ovulation time was 29.3 ± 0.5 h, which mostly occurred between 28 and 30 h after GnRH injection. However, all cows in the Saline group ovulated later than 36 h post-injection, with an average time of 52.7 ± 8.6 h. There was no difference in preovulatory follicle diameter between the two groups (16.8 ± 0.5 and 17.3 ± 0.5 mm for GnRH and saline groups, respectively). Although ovulation rate was not correlated with treatment, the rate within 48 h of GnRH injection (93.3%) tended to be higher compared with that in the Saline group (60.0%). Thus, GnRH administration increased ovulation rate following complete luteolysis induced by two low doses of PGF2α. These results indicate that this simple protocol for dairy cows is an effective alternative to timed artificial insemination programs in the field.
本研究调查了促性腺激素释放激素（GnRH）对经两次低剂量前列腺素（PG）F2α诱导完全黄体溶解后的泌乳奶牛排卵反应的影响。选取处于泌乳45至65天的奶牛（n = 18头），通过改良的Ovsynch - 48方案（GnRH - 7天 - 375μg PGF2α - 1天 - 250μg PGF2α - 1天 - GnRH）进行同期发情处理，共历经23个发情周期。在同期发情排卵9 - 10天后的实验第1阶段，将同期发情的奶牛（n = 16头）随机分为GnRH组和生理盐水组。在第0天和第1天（第0天 = 首次注射PGF2α），奶牛分别接受375μg和250μg PGF2α处理。在第2天，GnRH组和生理盐水组的奶牛分别注射250μg GnRH或2.5mL 0.9%生理盐水。从第0天至第3天每天测定血清孕酮（P4）水平，并通过超声监测黄体（CL）的变化以评估完全黄体溶解情况。通过超声检查评估排卵前卵泡直径和排卵反应。在第2阶段，奶牛的处理方式与第1阶段相反。同期发情率为69.6%（16/23）。在第1阶段和第2阶段，奶牛均出现了完全黄体溶解，P4浓度<1ng/mL或剩余CL面积<50%。平均排卵时间为29.3±0.5小时，大多发生在注射GnRH后28至30小时之间。然而，生理盐水组的所有奶牛排卵时间均晚于注射后36小时，平均时间为52.7±8.6小时。两组排卵前卵泡直径无差异（GnRH组和生理盐水组分别为16.8±0.5mm和17.3±0.5mm）。虽然排卵率与处理方式无关，但GnRH注射后48小时内的排卵率（93.3%）相较于生理盐水组（60.0%）有升高趋势。因此，在两次低剂量PGF2α诱导完全黄体溶解后，注射GnRH可提高排卵率。这些结果表明，这种针对奶牛的简单方案是牧场定时人工授精程序的一种有效替代方法。
