J Anim Sci. 2017 Nov;95(11):5105-5111. doi: 10.2527/jas2017.1805.
Our objective was to determine which of 2 split-time AI programs applied to suckled beef cows would result in greater pregnancy risk. Suckled beef cows (n = 1,062) at 12 locations in 4 states (CO, KS, MY, and WA) were enrolled. Cows were treated on d -7 with a progesterone insert concurrent with 100 µg GnRH and on d 0 with 25 mg PGF plus removal of the insert. Estrus-detection patches were affixed to cows at insert removal. The study was designed as a completely randomized experiment of 2 treatment combinations. Within location and balanced for parity (primiparous vs. multiparous), cows were assigned randomly to 2 treatment times (55 vs. 65 h after CIDR insert removal) at which time estrus-detection patches were assessed. Estrus was defined to have occurred when an estrus-detection patch was > 50% colored (activated). Cows determined to be in estrus were inseminated at either 55 or 65 h, whereas the residual nonestrous cows in both treatment times received GnRH at 55 or 65 h but were inseminated 20 h later at 75 or 85 h, respectively. Pregnancy outcomes were determined at 36 d after AI and at the end of the breeding season. Thus, pregnancy outcomes of interest were compared between the 55 + 75-h treatment combination and that of the 65+85-h combination. Expression of estrus was greater ( = 0.001) by 65 h after PGF than by 55 h (62.0% vs. 41.9%), respectively, and this proportion was influenced by parity (time x parity interaction; = 0.006). As a result, proportionally more ( < 0.001) cows received the timed AI at 75 than 85 h (59.4% vs. 40.6%). Similar proportions of cows not in estrus by 55 or 65 h were detected in estrus by 75 or 85 h (40.1% vs. 39.3%), respectively. The cumulative proportion of cows in estrus by 75 h was less ( < 0.001) than that by 85 h (66.7% vs. 76.7%), respectively. Pregnancy risks at 36 d differed among treatments, with cows detected in estrus and inseminated at 55 or 65 h having greater pregnancy risks than their time-inseminated herd mates at 75 or 85 h (62.3% vs.49.7%), respectively. Overall pregnancy risk for cows in the 65+85-h treatment combination was greater at 36 d than for cows in the 55 + 75-h treatment combination (61.0% vs. 51.4%), respectively. We conclude that the 65 + 85-h treatment combination produced more pregnancies than the 55 + 75-h combination, but its implementation may be somewhat less convenient in terms of cow handling times.
我们的目标是确定应用于哺乳期奶牛的 2 种分时人工智能程序中，哪一种会导致更高的妊娠风险。来自 4 个州（科罗拉多州、堪萨斯州、密歇根州和华盛顿州）的 12 个地点的 1062 头哺乳期奶牛被纳入研究。奶牛在第-7 天用孕酮插入物处理，同时给予 100μg GnRH，第 0 天用 25mg PGF 处理并取出插入物。在取出插入物时，将发情检测贴片贴在奶牛身上。该研究设计为 2 种处理组合的完全随机实验。在位置和产次（初产和经产）平衡的情况下，将奶牛随机分配到 2 种处理时间（CIDR 插入物去除后 55 或 65 小时），此时评估发情检测贴片。当发情检测贴片的颜色（激活）超过 50%时，即可确定发情。确定发情的奶牛在 55 或 65 小时进行授精，而在两个处理时间的剩余非发情奶牛在 55 或 65 小时给予 GnRH，但在 75 或 85 小时进行授精。在人工授精后 36 天和配种季节结束时确定妊娠结果。因此，比较了 55 + 75 小时治疗组合和 65 + 85 小时治疗组合之间的妊娠结果。PGF 后 65 小时的发情表达高于 55 小时（分别为 62.0%和 41.9%）（= 0.001），并且这种比例受产次影响（时间 x 产次交互作用；= 0.006）。因此，在 75 小时接受定时授精的奶牛比例（= 0.001）高于 85 小时（59.4%比 40.6%）。在 55 或 65 小时未发情的奶牛中，有相似比例的奶牛在 75 或 85 小时发情（分别为 40.1%和 39.3%）。在 75 小时发情的奶牛比例（= 0.001）低于 85 小时（分别为 66.7%和 76.7%）。在处理之间，发情和在 55 或 65 小时授精的奶牛的妊娠风险不同，与在 75 或 85 小时授精的同群奶牛相比，妊娠风险更高（分别为 62.3%和 49.7%）。在 36 天时，65 + 85 小时治疗组合的奶牛妊娠风险高于 55 + 75 小时治疗组合（分别为 61.0%和 51.4%）。我们得出结论，65 + 85 小时的治疗组合产生的妊娠多于 55 + 75 小时的治疗组合，但就奶牛处理时间而言，其实施可能稍微不太方便。
