The objective was to optimize fertility in a modified 5-d CO-Synch protocol by altering the timing of GnRH administration and AI. Holstein heifers (14-16 mo) received a controlled internal drug releasing device (CIDR) on d 0 and on d 5, CIDR were removed, prostaglandin F2α was administered and estrus detection patches were applied. Estrus was detected at 36, 48, 56 and 72 h after CIDR removal. In Experiment 1, control heifers (n = 195) received GnRH concurrent with timed-AI (TAI) 72 h after CIDR removal, regardless of expression of estrus. Treatment heifers expressing estrus at 36 or 48 h were AI at 56 h (n = 101) and the remaining heifers were randomly assigned to one of two groups: GnRH administration at 56 h and TAI at 72 h (GnRH56, n = 147) or GnRH administered concurrently with TAI at 72 h (GnRH72, n = 148). In Experiment 2, heifers expressing estrus at 36 or 48 h following CIDR removal were AI at 56 h (n = 118) and the remaining heifers were either TAI at 72 h (TAI72, n = 102) or 80 h (TAI80, n = 102), with only heifers not displaying estrus by TAI given GnRH concurrent with AI. All heifers were inseminated with sex-sorted semen and pregnancy diagnosis was performed at 28 d following TAI. In Experiment 1, estrus rate (P = 0.81) and pregnancy per AI (P/AI; P = 0.34) did not differ among control, GnRH56 and GnRH72 groups, so GnRH56 and GnRH72 groups were combined into one split-TAI (STAI) group. The P/AI was greater in heifers displaying estrus by 48 h compared to those not displaying estrus and receiving GnRH in both groups (69.5 vs. 31.3%; P < 0.01) and there was a tendency for P/AI to increase in STAI heifers displaying estrus compared to control heifers displaying estrus (73.3 vs. 62.1%; P = 0.10). In Experiment 2, the estrus rate was increased in TAI80 compared to TAI72 heifers (81.4 vs. 62.7%, P < 0.01); however, there was no difference in P/AI (P = 0.74). Heifers displaying estrus in the TAI72 group had a greater P/AI than heifers not displaying estrus in either group (P < 0.01) and tended to have a greater P/AI than heifers in estrus in the TAI80 group (87.5 vs. 69.9%, P = 0.07). Across both experiments, P/AI was increased in heifers that displayed estrus before AI compared with heifers that did not and performing a STAI tended to increase P/AI in heifers that displayed estrus before AI. Other attempts made to optimize P/AI in the modified 5-d CO-Synch protocol by altering the timing of GnRH administration and/or AI were unsuccessful.

中文翻译：

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改变 GnRH 给药和人工授精时间的影响在改良的 5 天 CO-Synch 协议中使用奶牛的性别分选精液

目的是通过改变 GnRH 给药和 AI 的时间，在修改后的 5 天 CO-Synch 协议中优化生育能力。荷斯坦小母牛（14-16 个月）在第 0 天和第 5 天接受受控内部药物释放装置（CIDR），移除 CIDR，施用前列腺素 F2α 并应用发情检测贴剂。在去除 CIDR 后 36、48、56 和 72 小时检测到发情。在实验 1 中，对照小母牛（n = 195）在去除 CIDR 后 72 小时同时接受 GnRH 和定时 AI（TAI），无论发情的表达如何。在 36 或 48 小时表达发情的治疗小母牛在 56 小时时为 AI（n = 101），其余的小母牛随机分配到两组之一：56 小时 GnRH 给药和 72 小时 TAI（GnRH56，n = 147）或GnRH 在 72 小时时与 TAI 同时给药（GnRH72，n = 148）。在实验 2 中，在去除 CIDR 后 36 或 48 小时表达发情的小母牛在 56 小时时为 AI（n = 118），其余的小母牛在 72 小时（TAI72，n = 102）或 80 小时（TAI80，n = 102）时为 TAI，其中只有在 GnRH 与 AI 并发的情况下，TAI 不显示发情的小母牛。所有小母牛都用性别分选的精液进行授精，并在 TAI 后 28 天进行妊娠诊断。在实验 1 中，每个 AI 的发情率（P = 0.81）和妊娠（P/AI；P = 0.34）在对照组、GnRH56 和 GnRH72 组之间没有差异，因此 GnRH56 和 GnRH72 组被合并为一个分裂 TAI（STAI）团体。与未显示发情并接受 GnRH 的小母牛相比，48 小时后显示发情的小母牛的 P/AI 更高（69.5% vs. 31.3%；P < 0。01) 并且与显示发情的对照小母牛相比，显示发情的 STAI 小母牛的 P/AI 有增加的趋势（73.3 对 62.1%；P = 0.10）。在实验 2 中，与 TAI72 小母牛相比，TAI80 的发情率增加（81.4 对 62.7%，P < 0.01）；然而，P/AI 没有差异（P = 0.74）。在 TAI72 组中显示发情的小母牛的 P/AI 高于任一组中未显示发情的小母牛（P < 0.01），并且趋向于比 TAI80 组中发情的小母牛具有更高的 P/AI（87.5% vs. 69.9%， P = 0.07）。在这两个实验中，与未在 AI 之前发情的小母牛相比，在 AI 之前显示发情的小母牛的 P/AI 增加，并且执行 STAI 倾向于增加在 AI 之前显示发情的小母牛的 P/AI。