Livestock Research Branch, Alberta Agriculture and Rural Development, Edmonton, AB, T6H 5T6, Canada.
J Dairy Sci. 2013;96(12):7640-8. doi: 10.3168/jds.2013-6750. Epub 2013 Oct 4.
A protocol for presynchronization of ovarian status with 2 injections of PGF2α given 14 d apart, with the last PGF2α injection given 12 or 14 d before Ovsynch increases pregnancy per artificial insemination (P/AI) in dairy cows. We determined the efficacy of reducing the interval from the last PGF2α injection (500 μg of cloprostenol) of presynchronization to initiation of Ovsynch on response to treatment and P/AI. Lactating dairy cows were assigned to an Ovsynch protocol, with the initial injection of GnRH given either 9 (PRE-9; n=135) or 12d (PRE-12; n=135) after the second PGF2α injection of presynchronization. The Ovsynch protocol consisted of 2 injections of 100 μg of GnRH given 9 d apart and 1 injection of PGF2α given 7 d after the initial GnRH injection, and cows were subjected to timed artificial insemination (TAI; 70±3.5 DIM) approximately 16 h after the second GnRH injection. Body condition score (1-5 scale) was recorded at TAI. Blood samples were taken for progesterone determination at the PGF2α injection of Ovsynch, at TAI, and at 11 d after TAI. Ultrasonographic examinations were done in all cows at the second PGF2α injection of presynchronization, initial GnRH injection, PGF2α injection of Ovsynch, at TAI, and 24 h after TAI for cyclicity status and ovarian responses to treatments, and at 32 and 60 d after TAI for confirmation of pregnancy. Overall, 29 cows (10.7%) were determined acyclic or cystic and excluded from the study. The percentage of cows responding to initial GnRH injection (62.2 vs. 61.5%) did not differ between PRE-9 and PRE-12 but more cows in the PRE-9 group failed to respond to PGF2α treatment of Ovsynch compared with PRE-12 (22.7 vs. 10.7%). Body condition score at TAI (2.9±0.02) and mean ovulatory follicle diameter (16.4±0.2 mm) were not different between treatments. Overall P/AI at 32 d was reduced in PRE-9 (33.6%) compared with PRE-12 (44.3%) but pregnancy losses (5.0 vs. 3.7%) did not differ between treatments. Primiparous cows in the PRE-12 group had higher mean progesterone concentration 11 d after TAI and greater P/AI 32 after TAI than primiparous cows in the PRE-9 group (6.4±0.5 vs. 4.6±0.5 ng/mL and 55.8 vs. 30.0%, respectively). In conclusion, reducing the interval from the last PGF2α injection of the presynchronization treatment to initiation of Ovsynch (from 12 to 9 d) did not affect ovulatory response to initial GnRH injection but reduced response to PGF2α injection of Ovsynch and P/AI at 32 and 60 d after TAI. The reduction in P/AI was particularly evident in primiparous cows of the PRE-9 group.
一项方案是在相隔 14 天的时间内给予两次前列腺素 F2α（PGF2α）注射，以同步卵巢状态，最后一次 PGF2α 注射在 Ovsynch 前 12 或 14 天进行，这可以提高奶牛人工授精的妊娠率（P/AI）。我们确定了减少同步化最后一次 PGF2α 注射（500μg氯前列醇）到 Ovsynch 开始之间的间隔对治疗反应和 P/AI 的影响。泌乳奶牛被分配到 Ovsynch 方案中，初始 GnRH 注射分别在同步化的第二次 PGF2α 注射后 9 天（PRE-9；n=135）或 12 天（PRE-12；n=135）进行。Ovsynch 方案包括两次间隔 9 天的 100μg GnRH 注射和一次 PGF2α 注射，在初始 GnRH 注射后 7 天进行，并且在第二次 GnRH 注射后大约 16 小时进行定时人工授精（TAI；70±3.5 DIM）。在 TAI 时记录体况评分（1-5 分制）。在 Ovsynch 的 PGF2α 注射时、TAI 时和 TAI 后 11 天时采集血液样本以测定孕酮。所有奶牛在同步化的第二次 PGF2α 注射、初始 GnRH 注射、Ovsynch 的 PGF2α 注射、TAI 时以及 TAI 后 24 小时进行超声检查，以检查排卵状态和卵巢对治疗的反应，并在 TAI 后 32 天和 60 天进行超声检查以确认妊娠。总体而言，29 头奶牛（10.7%）被确定为无周期或囊性，被排除在研究之外。对初始 GnRH 注射的反应率（62.2%对 61.5%）在 PRE-9 和 PRE-12 之间没有差异，但与 PRE-12 相比，PRE-9 组中更多的奶牛对 Ovsynch 的 PGF2α 治疗没有反应（22.7%对 10.7%）。TAI 时的体况评分（2.9±0.02）和平均排卵卵泡直径（16.4±0.2mm）在两种处理方法之间没有差异。总体而言，PRE-9（33.6%）的 32 天 P/AI 低于 PRE-12（44.3%），但两种处理方法的妊娠损失（5.0%对 3.7%）没有差异。PRE-12 组的初产奶牛在 TAI 后 11 天的平均孕酮浓度较高，TAI 后 32 天的 P/AI 也较高，分别为 6.4±0.5 ng/mL 和 4.6±0.5 ng/mL（6.4±0.5 ng/mL 和 4.6±0.5 ng/mL）和 55.8%对 30.0%（分别）。总之，将同步化治疗的最后一次 PGF2α 注射与 Ovsynch 开始之间的间隔从 12 天缩短到 9 天不会影响初始 GnRH 注射的排卵反应，但会降低 Ovsynch 的 PGF2α 注射反应和 TAI 后 32 天和 60 天的 P/AI。这种 P/AI 的降低在 PRE-9 组的初产奶牛中尤为明显。
