The main objective was to investigate the effects of timed‐AI protocols versus AI following oestrus detection on circulating progesterone (P4) and embryo survival after first service in Holstein cows. Cycling status was determined by ultrasonography and by plasma P4 concentrations 14 and 26 days after calving, and only cows with a corpus luteum and/or P4 ≥ 1 ng/ml were used. Cows were randomly allocated to one of three types of breeding: DO (n = 80), received GnRH‐7d‐PGF2α‐3d‐GnRH and Ovsynch56 was initiated 7 days later; G7G (n = 70), received PGF2α‐2d‐GnRH and Ovsynch56 (GnRH‐7d‐PGF2α‐56h‐GnRH‐16h‐AI) was initiated 7 days later; or AI based on oestrus detection, EDAI (n = 60). Progesterone was also determined at AI and 8, 16, 18 and 20 days after AI; ISG15 and MX2 mRNA abundance were determined 16 days after AI. Mean plasma P4 at AI was greater in the EDAI group compared with DO and G7G groups, while after AI, P4 was greater in DO and G7G groups compared with EDAI group. However, the percentage of cows with a concentration of P4 < 0.8 ng/ml at AI did not differ among groups. Relative mRNA abundance of ISG15 and MX2 was greater in the DO and G7G groups compared to those in EDAI group. Pregnancy per AI 16, 32 and 60 days after AI was greater (p < .05) in cows in the DO group compared with those in EDAI group (47.5%, 38.8% and 36.3% vs. 30.0%, 21.7% and 15.0%). Pregnancy losses between 16 and 60 days after AI were greater (p < .05) in cows in the EDAI (50.0%) group compared to those subjected to DO (23.7%) or G7G (24.1%). In conclusion, the use of timed‐AI synchronization protocols resulted in greater circulating P4 concentrations post‐AI and greater embryo survival following first service in lactating Holstein cows.

中文翻译：

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育种类型对泌乳荷斯坦奶牛首次人工授精后胚胎存活的影响

主要目的是研究定时 AI 协议与发情检测后 AI 对荷斯坦奶牛首次服务后循环孕酮 (P4) 和胚胎存活率的影响。通过超声检查和产犊后 14 天和 26 天的血浆 P4 浓度确定循环状态，并且仅使用具有黄体和/或 P4 ≥ 1 ng/ml 的奶牛。奶牛被随机分配到三种育种类型之一：DO（n  = 80），接受 GnRH-7d-PGF2α-3d-GnRH，7 天后启动 Ovsynch56；G7G ( n  = 70)，接受 PGF2α-2d-GnRH 和 Ovsynch56 (GnRH-7d-PGF2α-56h-GnRH-16h-AI) 7 天后；或基于发情检测的人工智能，EDAI（n = 60）。在 AI 和 AI 后 8、16、18 和 20 天也测定了孕酮；在 AI 后 16 天确定 ISG15 和 MX2 mRNA 丰度。与 DO 和 G7G 组相比，EDAI 组在 AI 时的平均血浆 P4 更大，而在 AI 后，与 EDAI 组相比，DO 和 G7G 组的 P4 更大。然而，AI 浓度 P4 < 0.8 ng/ml 的奶牛百分比在各组之间没有差异。与 EDAI 组相比，DO 和 G7G 组中 ISG15 和 MX2 的相对 mRNA 丰度更高。 与 EDAI 组相比，DO 组奶牛在AI 后 16、32 和 60 天的每次 AI 妊娠率更高（p < .05）（47.5%、38.8% 和 36.3% 对 30.0%、21.7% 和 15.0%） ）。AI 后 16 至 60 天的妊娠损失更大（p < .05) 在 EDAI (50.0%) 组中的奶牛与那些接受 DO (23.7%) 或 G7G (24.1%) 的奶牛相比。总之，在泌乳荷斯坦奶牛首次使用后，使用定时 AI 同步协议导致 AI 后循环 P4 浓度更高，胚胎存活率更高。