The objective of this study was to evaluate the impact of early progesterone removal on pregnancy rates to fixed-time artificial insemination (FTAI) in presynchronized beef cows. Postpartum beef cows (n = 922; body condition score = 4.9 ± 0.77; days postpartum = 77.3 ± 20.77 d) from 7 locations were enrolled in a completely randomized design. Within location, cows were stratified by parity and days postpartum before being randomly assigned to 1 of 2 treatments: 1) 7&7 Synch: Cows received a controlled internal drug release insert (CIDR) and a 25-mg injection of prostaglandin F2α (PG1; d 0). Cows received 100 μg of GnRH on d 7 and the CIDR was removed 7 d later, concurrently with a second prostaglandin F2α (PG2) injection (d 14). Cows received a second injection of GnRH and were FTAI 60-66 h after PG2 (d 17); 2) 7&6 Synch: Cows received the same treatment as 7&7 Synch cows; however, CIDR removal and PG2 were performed on d 13, and cows were FTAI 60-66 h after CIDR removal. Ovarian ultrasonography was performed to determine follicle diameter and CL presence at PG2 and FTAI in a subset of cows (n = 40). Estrus detection patches were utilized to evaluate estrus expression between PG2 and FTAI. Pregnancy diagnosis was performed 28-35 d after FTAI. Cows exposed to the 7&7 Synch tended to have larger follicle diameter at PG2 compared with 7&6 Synch cows (P = 0.09); however, there were no differences in follicle diameter at FTAI. Cows that expressed estrus tended to have larger follicle diameter at FTAI compared with cows that failed to express estrus (P = 0.10). Follicular growth between PG2 and FTAI, percentage of cows with a corpus luteum at PG2, and ovulation rate were not impacted by treatment (P ≥ 0.56). No differences were determined between treatments for estrus expression (7&7 Synch: 77.1 ± 5.91; 7&6 Synch: 74.6 ± 6.28; P = 0.50) or pregnancy rates to FTAI (7&7 Synch: 60.1 ± 4.32; 7&6 Synch: 58.2 ± 4.26; P = 0.69). In conclusion, early removal of progesterone did not impact pregnancy rates in presynchronized beef cows. Thus, the 7&6 Synch protocol described herein may be used as an alternative to the conventional 7&7 Synch protocol without compromising fertility.

中文翻译：

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15 早期去除黄体酮对预同步肉牛卵泡发育、发情表达和妊娠率的影响

本研究的目的是评估提前去除黄体酮对预同步肉牛固定时间人工授精 (FTAI) 妊娠率的影响。来自 7 个地点的产后肉牛（n = 922；身体状况评分 = 4.9 ± 0.77；产后天数 = 77.3 ± 20.77 天）被纳入完全随机设计。在地点内，奶牛根据胎次和产后天数进行分层，然后随机分配到 2 种治疗中的 1 种：1) 7&7 同步：奶牛接受受控体内药物释放插入物 (CIDR) 和 25 毫克前列腺素 F2α 注射 (PG1；d 0）。奶牛在第 7 天接受 100 μg GnRH，7 天后去除 CIDR，同时注射第二次前列腺素 F2α (PG2)（第 14 天）。奶牛接受第二次 GnRH 注射，并在 PG2 后 60-66 小时进行 FTAI（第 17 天）；2）7&6 Synch：奶牛接受与7&7 Synch奶牛相同的治疗；然而，CIDR 去除和 PG2 在第 13 天进行，奶牛在 CIDR 去除后 60-66 小时进行 FTAI。对一组奶牛 (n = 40) 进行卵巢超声检查，以确定 PG2 和 FTAI 时的卵泡直径和 CL 存在情况。利用发情检测贴片来评估 PG2 和 FTAI 之间的发情表达。FTAI后28-35天进行妊娠诊断。与 7&6 Synch 奶牛相比，接触 7&7 Synch 的奶牛在 PG2 时往往具有更大的卵泡直径 (P = 0.09)；然而，FTAI 时卵泡直径没有差异。与未表达发情的奶牛相比，表达发情的奶牛在 FTAI 时往往具有更大的卵泡直径（P = 0.10）。PG2 和 FTAI 之间的卵泡生长、PG2 时具有黄体的奶牛百分比以及排卵率不受治疗影响（P ≥ 0.56）。发情表达处理（7&7 Synch：77.1 ± 5.91；7&6 Synch：74.6 ± 6.28；P = 0.50）或 FTAI 妊娠率（7&7 Synch：60.1 ± 4.32；7&6 Synch：58.2 ± 4.26；P = 0.50）治疗之间没有差异。 0.69）。总之，早期去除黄体酮不会影响预同步肉牛的妊娠率。因此，本文描述的7&6 Synch方案可用作常规7&7 Synch方案的替代方案，而不损害生育力。