The aim of this study was to examine the effect of a single administration of human chorionic gonadotrophin (hCG) during the establishment of the corpus luteum (CL) on progesterone (P4) concentration and pregnancy per artificial insemination (P/AI) in lactating dairy cows. Postpartum spring-calving lactating dairy cows (n = 800; mean ± SD days in milk and parity were 78.5 ± 16.7 and 2.3 ± 0.8, respectively) on 3 farms were enrolled on the study. All cows underwent the same fixed-time AI (FTAI) protocol involving a 7-d progesterone-releasing intravaginal device with gonadotrophin-releasing hormone (GnRH) administration at device insertion, prostaglandin at device removal followed by GnRH 56 h later, and AI 16 h after the second GnRH injection. Cows were blocked on days postpartum, body condition score, and parity and randomly assigned to receive either 3,000 IU of hCG 2 d after FTAI or no further treatment (control). Blood samples were collected on d 7 and 14 postestrus by coccygeal venipuncture on a subset of 204 cows to measure serum P4 concentration, and pregnancy was diagnosed by ultrasonography approximately 30 and 70 d after FTAI. Administration of hCG caused an increase in circulating P4 concentrations compared with the control treatment on d 7 (+22.2%) and d 14 (+25.7%). The P/AI at 30 d after FTAI was affected by treatment, farm, body condition score, and calving to service interval. Overall, administration of hCG decreased P/AI (46.3% vs. 55.1% for the control). Among cows that did not become pregnant following AI, a greater proportion of control cows exhibited a short repeat interval (≤17 d) compared with cows treated with hCG (8.6% vs. 2.8%, respectively). In addition, the percentages of cows pregnant at d 21 (59.6% vs. 52.0%) and d 42 (78.3% vs. 71.9%) were greater in control than in hCG-treated cows. The overall incidence of embryo loss was 10.7% and was not affected by treatment. There was a tendency for an interaction between treatment and CL status at synchronization protocol initiation for both P4 concentration and P/AI. In conclusion, administration of hCG 2 d after FTAI increased circulating P4 concentrations. Unexpectedly, cows treated with hCG had lower fertility; however, this negative effect on fertility was manifested primarily in cows lacking a CL at the onset of the synchronization protocol.

这项研究的目的是要检查在建立黄体（CL）期间单次施用人绒毛膜促性腺激素（hCG）对泌乳奶牛每次人工授精（P / AI）孕酮（P4）浓度和妊娠的影响。牛。研究纳入了3个农场的产后春季产犊泌乳奶牛（n = 800；牛奶和胎次的平均±SD天数分别为78.5±16.7和2.3±0.8）。所有奶牛均接受相同的固定时间AI（FTAI）方案，包括在植入器械时使用促性腺激素释放激素（GnRH）施用7d孕激素释放阴道内装置，在取出器械时使用前列腺素，然后在56 h后使用GnRH和AI 16第二次GnRH注射后h。母牛在产后几天，身体状况评分，且均等，并被随机分配为在FTAI后2 d接受3,000 IU的hCG或不进行进一步治疗（对照）。在204名奶牛的子集上通过尾静脉穿刺法在发情后的第7天和第14天采集血样，以测量血清P4浓度，并在FTAI后约30和70天通过超声检查诊断怀孕。与d 7（+ 22.2％）和d 14（+ 25.7％）的对照治疗相比，hCG的给药引起循环P4浓度增加。FTAI后30 d的P / AI受治疗，农场，身体状况评分以及分娩至服务间隔的影响。总体而言，hCG的使用降低了P / AI（46.3％，而对照组为55.1％）。与经hCG处理的母牛相比，在AI后未怀孕的母牛中，较大比例的对照母牛表现出较短的重复间隔（≤17d）。分别为6％和2.8％）。另外，在第21天（第59天对52.0％对52.0％）和第42天（78.3％对71.9％）的怀孕母牛的百分比比用hCG治疗的母牛高。胚胎丢失的总发生率为10.7％，并且不受治疗的影响。对于P4浓度和P / AI，在同步协议启动时治疗和CL状态之间存在相互作用的趋势。总之，FTAI后2 d给予hCG可增加循环P4浓度。出乎意料的是，用hCG处理过的母牛的生育力较低。但是，这种对生育力的负面影响主要表现在同步协议开始时没有CL的母牛身上。对照中，有9％的人比经hCG处理的牛更大。胚胎丢失的总发生率为10.7％，并且不受治疗的影响。对于P4浓度和P / AI，在同步协议启动时治疗和CL状态之间存在相互作用的趋势。总之，FTAI后2 d给予hCG可增加循环P4浓度。出乎意料的是，用hCG处理过的母牛的生育力较低。但是，这种对生育力的负面影响主要表现在同步协议开始时没有CL的母牛身上。对照中，有9％的人比经hCG处理的牛更大。胚胎丢失的总发生率为10.7％，并且不受治疗的影响。对于P4浓度和P / AI，在同步协议启动时治疗和CL状态之间存在相互作用的趋势。总之，FTAI后2 d给予hCG可增加循环P4浓度。出乎意料的是，用hCG处理过的母牛的生育力较低。但是，这种对生育力的负面影响主要表现在同步协议开始时没有CL的母牛身上。FTAI后2 d给予hCG可增加循环P4浓度。出乎意料的是，用hCG处理过的母牛的生育力较低。但是，这种对生育力的负面影响主要表现在同步协议开始时没有CL的母牛身上。FTAI后2 d给予hCG可增加循环P4浓度。出乎意料的是，用hCG处理过的母牛的生育力较低。但是，这种对生育力的负面影响主要表现在同步协议开始时没有CL的母牛身上。