The primary objective of this study was to determine if estrus activity and reproductive tract size and position score (SPS) are associated with pregnancy outcomes in Bos indicus (Nelore) and Bos taurus (Angus) beef cows. In study 1, multiparous Nelore cows (n = 1,280) were artificially inseminated at a fixed time (FTAI, day 0) using an estradiol and progesterone (P4)-based estrus synchronization protocol. In study 2, multiparous Angus cows (n = 764) were artificially inseminated at a fixed time (FTAI, day 0) using a gonadotropin-releasing hormone and P4-based estrus synchronization protocol. Estrus activity was assessed using Estrotect heat detector patches and scored on day 0 using the following scoring system: 0 (patch was lost, most likely due to repeated mounting), 1 (<25% activation), 2 (≥25%, <50% activation), 3 (≥50%, <75% activation), or 4 (>75% activation) where patch scores of 1 and 2 signified no or limited estrus activity, whereas scores of 0, 3, and 4 had increased estrus activity. Reproductive tract SPS were assigned on day 0 as SPS1: small and compact resting within the pelvic cavity; SPS2: intermediate, resting partially outside the pelvic cavity; and SPS3: larger and resting outside the pelvic cavity. Pregnancy diagnosis was performed by ultrasound on day 30 and 100 after FTAI. Cows were determined as undergoing pregnancy loss if a viable embryo with heartbeat was detected at day 30 but was no longer present at day 100. Pregnancy rate at day 30 was influenced by estrus activity and SPS in both Nelore (P = 0.004) and Angus (P = 0.009) cows. Specifically, cows with smaller reproductive tracts (SPS1) had greater (P < 0.001) pregnancy rate when estrus was expressed before FTAI. There was no effect of estrus activity nor reproductive tract size on pregnancy loss between day 30 and 100 for both breeds. In summary, estrus activity before FTAI may influence reproductive outcomes differently depending on size and position of the reproductive tract at time of breeding.

中文翻译：

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短通讯：发情活动和生殖道大小和位置得分对 Bos indicus 和 Bos taurus 哺乳肉牛生育力的影响

本研究的主要目的是确定发情活动和生殖道大小和位置评分 (SPS) 是否与 Bos indicus (Nelore) 和 Bos taurus (Angus) 肉牛的妊娠结局相关。在研究 1 中，使用基于雌二醇和黄体酮 (P4) 的发情同步方案在固定时间（FTAI，第 0 天）对经产 Nelore 奶牛 (n = 1,280) 进行人工授精。在研究 2 中，经产安格斯奶牛 (n = 764) 在固定时间（FTAI，第 0 天）使用促性腺激素释放激素和基于 P4 的发情同步方案进行人工授精。使用 Estrotect 热探测器贴片评估发情期活动，并在第 0 天使用以下评分系统评分：0（贴片丢失，很可能是由于重复安装），1（<25% 激活），2（≥25%，< ;50% 激活), 3 (≥50%, < 75% 激活）或 4（>75% 激活），其中 1 和 2 的补丁分数表示没有或有限的发情活动，而 0、3 和 4 的分数表示发情活动增加。生殖道 SPS 在第 0 天被指定为 SPS1：小而紧凑，位于盆腔内；SPS2：中间，部分位于盆腔外；SPS3：较大，位于盆腔外。在 FTAI 后第 30 天和第 100 天通过超声进行妊娠诊断。如果在第 30 天检测到有心跳但在第 100 天不再存在的存活胚胎，则奶牛被确定为流产。在 Nelore (P = 0.004) 和 Angus ( P = 0.009) 奶牛。具体而言，具有较小生殖道 (SPS1) 的奶牛具有更高的生殖道 (P < 0. 001) 在 FTAI 之前表达发情时的妊娠率。发情期活动和生殖道大小对两个品种在第 30 天到第 100 天的流产没有影响。总之，FTAI 之前的发情活动可能会根据繁殖时生殖道的大小和位置对生殖结果产生不同的影响。