There are multiple factors that contribute to reduced fertility in lactating dairy cows. Recently, a reproductive tract size and position score (SPS) system was developed as a management tool to identify dairy cows with decreased fertility. The aim of this study was to evaluate the association between the SPS on fertility outcomes such as ovulation failure, pregnancy per artificial insemination (P/AI), concentration of pregnancy-associated glycoproteins (PAGs), and pregnancy loss in lactating dairy cows. Primiparous and multiparous lactating Holstein cows (n = 869) were enrolled at two locations. Location 1 (Loc. 1) in Minas Gerais, Brazil (n = 613) and location 2 (Loc. 2) in Agassiz, British Columbia, Canada (n = 256). At the time of AI (d 0), cows were classified as SPS (small [SPS1], medium [SPS2], or large [SPS3] sized reproductive tract) and ovulation failure was determined at 48 h and 7 d post-AI via ultrasonography (Loc. 2 only). Blood samples were collected on d 24 and 31 of gestation for quantification of PAGs and pregnancy diagnosis was performed via ultrasonography at d 31 and 60 post-AI (Loc. 1) and at d 31 ± 3 and 60 ± 3 post-AI (Loc. 2). Cows diagnosed pregnant at d 31 post-AI but not pregnant at d 60 were defined to have undergone late embryonic pregnancy loss. Parity was found to impact SPS (P < 0.01), as primiparous cows had a higher frequency of SPS1 and lower frequency of SPS3 when compared with multiparous cows (SPS1: 42.6 vs. 15.0%; SPS3: 7.0 vs. 22.0%, respectively). Cows classified as SPS3 had greater ovulation failure at 48 h (P = 0.04) and 7 d post-AI (P = 0.05). Cows classified as SPS1 had greater P/AI when compared to SPS2 and SPS3 (45.9 ± 3.3 vs. 37.4 ± 2.6 and 29.1 ± 3.5%, respectively; P = 0.004). There was no interaction between parity and SPS on P/AI. Pregnancy loss between 31 and 60 d post-AI was increased in cows classified as SPS3 compared to SPS2 and SPS1 (24.3 ± 0.05 vs. 11.6 ± 0.02 and 9.4 ± 0.02%, respectively; P = 0.04). Cows classified as SPS1 and SPS2 had greater concentrations of PAGs at 31 d post-AI when compared to SPS3 at both Loc.1 (P < 0.01) and Loc. 2 (P < 0.01). There was no interaction between SPS and pregnancy loss on PAGs at 24 and 31 d post- AI for either Loc. 1 (P = 0.75 and P = 0.76, respectively) or Loc. 2 (P = 0.61 and P = 0.81, respectively). In conclusion, cows that were classified as SPS3 had greater ovulation failure, reduced P/AI, similar concentrations of PAG on d 24, but decreased on d 31, and a greater incidence of pregnancy loss. Thus, size and position of the reproductive tract is associated with fertility and this scoring system could be used to make reproductive management decisions on dairy operations.

中文翻译：

---

生殖道的大小和位置影响泌乳奶牛的生育结果和妊娠损失

有多种因素会导致泌乳奶牛的生育能力下降。最近，生殖道大小和位置评分 (SPS) 系统被开发作为管理工具来识别生育能力下降的奶牛。本研究的目的是评估 SPS 与排卵失败、每次人工授精 (P/AI)、妊娠相关糖蛋白 (PAG) 浓度和泌乳奶牛妊娠丢失等生育结果之间的关联。在两个地点招募了初产和经产泌乳荷斯坦奶牛（n = 869）。巴西米纳斯吉拉斯州的位置 1（位置 1）（n = 613）和加拿大不列颠哥伦比亚省阿加西的位置 2（位置 2）（n = 256）。在 AI (d 0) 时，奶牛被归类为 SPS（小型 [SPS1]、中型 [SPS2]、或大 [SPS3] 大小的生殖道）和排卵失败是在 AI 后 48 小时和 7 天通过超声检查确定的（仅位置 2）。在妊娠第 24 天和第 31 天收集血液样本以对 PAG 进行定量，并在 AI 后第 31 天和第 60 天（位置 1）以及 AI 后第 31 ± 3 天和第 60 ± 3 天（Loc . 2). 在 AI 后第 31 天诊断出怀孕但在第 60 天未怀孕的奶牛被定义为晚期胚胎流产。发现胎次会影响 SPS (P < 0.01)，因为与经产奶牛相比，初产奶牛具有更高的 SPS1 频率和更低的 SPS3 频率（SPS1：42.6 与 15.0%；SPS3：分别为 7.0 与 22.0%） . 归类为 SPS3 的奶牛在 AI 后 48 小时（P = 0.04）和 7 天（P = 0.05）排卵失败率更高。与 SPS2 和 SPS3 相比，分类为 SPS1 的奶牛具有更高的 P/AI（分别为 45.9 ± 3.3 与 37.4 ± 2.6 和 29.1 ± 3.5%；P = 0.004）。P/AI 上的奇偶校验和 SPS 之间没有交互作用。与 SPS2 和 SPS1 相比，分类为 SPS3 的奶牛在 AI 后 31 至 60 天之间的妊娠丢失增加（分别为 24.3 ± 0.05 与 11.6 ± 0.02 和 9.4 ± 0.02%；P = 0.04）。与 SPS3 相比，在 Loc.1 (P < 0.01) 和 Loc 后，分类为 SPS1 和 SPS2 的奶牛在 AI 后 31 天具有更高浓度的 PAG。2 (P < 0.01)。对于任一 Loc，在 AI 后 24 天和 31 天，SPS 与 PAG 上的流产之间没有相互作用。1（分别为 P = 0.75 和 P = 0.76）或 Loc。2（分别为 P = 0.61 和 P = 0.81）。总之，被归类为 SPS3 的奶牛排卵失败更严重，P/AI 降低，第 24 天 PAG 浓度相似，但在第 31 天下降，流产发生率更高。因此，生殖道的大小和位置与生育率相关，该评分系统可用于对乳品经营做出生殖管理决策。