Bishop B E, Thomas J M, Abel J M, Poock S E, Ellersieck M R, Smith M F, Patterson D J
Division of Animal Sciences, University of Missouri, Columbia, Missouri, USA; Department of Surgery and Medicine, University of Missouri, Columbia, Missouri, USA.
Division of Animal Sciences, University of Missouri, Columbia, Missouri, USA.
Theriogenology. 2016 Sep 1;86(4):1102-1110. doi: 10.1016/j.theriogenology.2016.03.043. Epub 2016 Apr 9.
Two experiments evaluated timing of GnRH administration in beef heifers and cows on the basis of estrous status during split-time artificial insemination (AI) after controlled internal drug release (CIDR) based protocols. In experiment 1, estrus was synchronized for 816 pubertal and prepubertal or peripubertal heifers using the 14-day CIDR-PGF2α (PG) protocol, and in experiment 2, estrus was synchronized for 622 lactating cows using the 7-day CO-Synch + CIDR protocol. For both experiments, estrus detection aids (Estrotect) were applied at PG, with estrus recorded at 66 and 90 hours after PG. Treatments were balanced across locations for heifers using reproductive tract score and weight; whereas for cows, treatments were assigned and balanced to treatment according to age, body condition score, and days postpartum. Timing of AI for heifers and cows was on the basis of estrus expression 66 hours after PG. Females in each treatment that exhibited estrus before 66 hours were inseminated at 66 hours, whereas AI was delayed 24 hours until 90 hours after PG for females failing to exhibit estrus before 66 hours. Females in treatment one received GnRH 66 hours after PG irrespective of estrus expression; however, in treatment 2, GnRH was administered coincident with delayed AI only to females not detected in estrus at 66 hours after PG. Among heifers, there was no effect of treatment on overall estrous response (P = 0.49) or AI pregnancy rate (P = 0.54). Pregnancy rate for heifers inseminated at 66 hours was not influenced by GnRH (P = 0.65), and there were no differences between treatments in estrous response during the 24 hours delay period (P = 0.22). Cows in treatment 2 had a greater (P = 0.04) estrous response during the 24-hour delay period resulting in a greater overall estrous response (P = 0.04), but this did not affect AI pregnancy rate at 90 hours (P = 0.51) or total AI pregnancy rate (P = 0.89). Pregnancy rate resulting from AI for cows inseminated at 66 hours was not influenced by GnRH (P = 0.50). In summary, when split-time AI was used with the 14-day CIDR-PG protocol in heifers or the 7-day CO-Synch + CIDR protocol in cows, administration of GnRH at AI to females that exhibited estrus before 66 hours after PG was not necessary. Furthermore, among heifers for which AI was delayed on the basis of failure to exhibit estrus before 66 hours after PG, timing of GnRH (66 vs. 90 hours after PG) was more flexible. Delayed administration of GnRH to 90 hours after PG coincident with AI for cows that failed to exhibit estrus before 66 hours improved overall estrous response; however, in this study, a corresponding increase in pregnancy rate resulting from AI was not observed.
两项试验基于在可控性内部药物释放（CIDR）方案后的分段人工授精（AI）期间的发情状态，评估了肉牛小母牛和母牛中促性腺激素释放激素（GnRH）的给药时间。在试验1中，使用14天的CIDR-前列腺素F2α（PG）方案使816头青春期及青春期前或接近青春期的小母牛发情同步；在试验2中，使用7天的同期发情+CIDR方案使622头泌乳母牛发情同步。对于两项试验，在注射PG时使用发情检测辅助工具（Estrotect），并在注射PG后66小时和90小时记录发情情况。对于小母牛，根据生殖道评分和体重在各地点平衡处理；而对于母牛，则根据年龄、体况评分和产后天数分配处理并使其在处理间平衡。小母牛和母牛的AI时间基于注射PG后66小时的发情表现。各处理中在66小时前表现出发情的雌性在66小时进行人工授精，而对于在66小时前未表现出发情的雌性，AI推迟24小时至注射PG后90小时。处理1中的雌性无论发情表现如何，均在注射PG后66小时接受GnRH；然而，在处理2中，仅对在注射PG后66小时未检测到发情的雌性在延迟AI时同时给予GnRH。在小母牛中，处理对总体发情反应（P = 0.49）或AI受胎率（P = 0.54）没有影响。在66小时进行人工授精的小母牛的受胎率不受GnRH影响（P = 0.65），并且在24小时延迟期内各处理间的发情反应没有差异（P = 0.22）。处理2中的母牛在24小时延迟期内有更大的（P = 0.04）发情反应，从而导致总体发情反应更大（P = 0.04），但这并未影响90小时时的AI受胎率（P = 0.51）或总AI受胎率（P = 0.89）。在66小时进行人工授精的母牛的AI受胎率不受GnRH影响（P = 0.50）。总之，当在小母牛中使用14天的CIDR-PG方案或在母牛中使用7天的同期发情+CIDR方案进行分段AI时，对于在注射PG后66小时前表现出发情的雌性，在AI时给予GnRH没有必要。此外，对于那些基于在注射PG后66小时前未表现出发情而延迟AI的小母牛，GnRH的给药时间（注射PG后66小时与90小时）更灵活。对于在66小时前未表现出发情的母牛，将GnRH延迟至注射PG后90小时并与AI同时进行可改善总体发情反应；然而，在本研究中，未观察到AI受胎率相应增加。
