Division of Animal Sciences, University of Missouri, Columbia, MO, 65211, USA.
Division of Animal Sciences, University of Missouri, Columbia, MO, 65211, USA; College of Veterinary Medicine, University of Missouri, Columbia, MO, 65211, USA.
Theriogenology. 2024 Jan 15;214:334-341. doi: 10.1016/j.theriogenology.2023.11.005. Epub 2023 Nov 8.
Two experiments were designed to evaluate later timepoints for fixed-time artificial insemination (FTAI) of beef heifers and cows, with the hypothesis that use of a later timepoint would allow a greater proportion of animals to express estrus prior to FTAI and result in greater conception rates among estrous females inseminated with sex-sorted semen. In Experiment 1, estrus was synchronized for 1640 heifers using the 14 d CIDR-PG protocol: insertion of an intravaginal progesterone-releasing insert (CIDR; 1.38 g progesterone) on Day -33 and removal on Day -19, and administration of prostaglandin F (PG; 500 μg cloprostenol sodium) on Day -3. Heifers were inseminated at one of three FTAI timepoints: 66 h, 70 h, or 74 h after PG administration. In Experiment 2, estrus was synchronized for 414 beef cows using the 7 & 7 Synch protocol: administration of PG coincident with CIDR insertion on Day -17, gonadotropin-releasing hormone (GnRH; 100 μg gonadorelin) on Day -10, and PG coincident with CIDR removal on Day -3. Cows were inseminated at one of two FTAI timepoints: 66 h or 72 h after PG administration. In both experiments, only animals that expressed estrus prior to FTAI were inseminated with sex-sorted semen. In Experiment 1, the proportion of heifers that expressed estrus prior to FTAI (66 h: 62 %; 70 h: 67 %; 74 h: 71 %) was greater when FTAI was performed at 74 h versus 66 h (P = 0.0097); however, conception rate of heifers that expressed estrus and were serviced with sex-sorted semen did not differ among treatments (P = 0.67; 66 h: 56 %; 70 h: 53 %; 74 h: 53 %). In Experiment 2, the proportion of cows expressing estrus prior to FTAI did not differ between treatments (P = 0.30; 66 h: 71 %; 72 h: 76 %). Additionally, conception rate of estrous cows inseminated with sex-sorted semen did not differ between treatments (P = 0.24; 66 h: 45 %; 72 h: 40 %). These results indicate that performing FTAI later following the 14 d CIDR-PG protocol increases the proportion of heifers that express estrus and are serviced with sex-sorted semen but does not improve conception rates. Later timing of FTAI following the 7 & 7 Synch protocol was not observed to increase the proportion of cows expressing estrus prior to FTAI or improve conception rates among estrous cows inseminated with sex-sorted semen. Together, these results provide further insight into optimal timing of FTAI when using sex-sorted semen.
设计了两项实验来评估牛的定时人工授精（FTAI）的后期时间点，假设使用较晚的时间点可以使更多的动物在 FTAI 前表现发情，并使使用性别分选精液授精的发情雌性的受孕率更高。在实验 1 中，1640 头小母牛使用 14d CIDR-PG 方案同步发情：在第-33 天插入阴道内释放孕激素的植入物（CIDR；1.38g 孕激素），在第-19 天取出，并在第-3 天给予前列腺素 F（PG；500μg 氯前列烯醇钠）。小母牛在 PG 给药后的三个 FTAI 时间点之一进行授精：66h、70h 或 74h。在实验 2 中，414 头肉牛使用 7&7 Synch 方案同步发情：PG 给药时同时插入 CIDR，在第-10 天给予促性腺激素释放激素（GnRH；100μg 戈那瑞林），在第-3 天 CIDR 取出时给予 PG。母牛在 PG 给药后的两个 FTAI 时间点之一进行授精：66h 或 72h。在这两个实验中，只有在 FTAI 前表现发情的动物才用性别分选精液授精。在实验 1 中，在 FTAI 进行 74h 时，比 66h 时表现发情的小母牛比例更大（66h：62%；70h：67%；74h：71%）（P=0.0097）；然而，表现发情并接受性别分选精液授精的小母牛的受孕率在处理之间没有差异（P=0.67；66h：56%；70h：53%；74h：53%）。在实验 2 中，发情前表现发情的母牛在处理之间的比例没有差异（P=0.30；66h：71%；72h：76%）。此外，用性别分选精液授精的发情母牛的受孕率在处理之间没有差异（P=0.24；66h：45%；72h：40%）。这些结果表明，在 14d CIDR-PG 方案之后进行较晚的 FTAI 可以增加表现发情并接受性别分选精液授精的小母牛的比例，但不能提高受孕率。在 7&7 Synch 方案之后，FTAI 的较晚时间点并没有观察到增加发情母牛的比例，也没有提高用性别分选精液授精的发情母牛的受孕率。总的来说，这些结果进一步深入了解了使用性别分选精液时 FTAI 的最佳时间。
