Department of Animal Science, Cornell University, Ithaca, NY 14853.
Dairy Health and Management Services, Lowville, NY 13367.
J Dairy Sci. 2020 Apr;103(4):3719-3729. doi: 10.3168/jds.2019-17585. Epub 2020 Feb 20.
The objective of this experiment was to compare time to pregnancy and proportion of cows not pregnant 210 d after first service for cows managed for second and subsequent artificial insemination (AI) services with a reproductive management program that promoted reinsemination at detected estrus (AIE) or a program that promoted timed AI (TAI). After first service, lactating Holstein cows were blocked by parity and randomly assigned to d 32 Resynch (D32R; n = 464) or AIE Resynch (AIER; n = 512). To determine the effect of management strategies on time to pregnancy and cows not pregnant by the end of a 210 d at-risk period after first AI service, cows remained in AIER and D32R until pregnancy or herd exit. Cows in D32R received a GnRH treatment 32 ± 3 d after AI (first treatment intervention; FTI). Nonpregnancy diagnosis was conducted 7 d later by transrectal ultrasonography when nonpregnant cows with a corpus luteum (CL) ≥15 mm completed the Resynch protocol (PGF, 56 h later GnRH, and 16 to 18 h later TAI) and cows without a CL (NoCL cows) were enrolled in a PreG-Ovsynch protocol (GnRH, 7 d later GnRH, 7 d later PGF, 56 h later GnRH, and 16 to 18 h TAI) to receive TAI. For the AIER treatment, nonpregnant cows with a CL ≥15 mm observed by transrectal ultrasonography 32 ± 3 d after AI (i.e., FTI) received PGF to induce estrus. Cows not AIE within 7 d were enrolled in Resynch (GnRH, 7 d later PGF, 56 h later GnRH, and 16 to 18 h TAI). Cows in the NoCL group in AIER were enrolled in PreG-Ovsynch. Detection of estrus was performed based on visual observation of behavioral signs of estrus and tail-paint removal. Binomial data were analyzed with logistic regression and time to event data with Cox's proportional regression. After the FTI, a greater proportion of cows were AIE in AIER than D32R (36.0 vs. 11.9%) and more cows were AIE within 7 d of the FTI for AIER (25.0%) than D32R (4.8%). Overall pregnancy per AI at 68 ± 3 d after AI did not differ (AIER = 35.5% vs. D32R = 34.7%). The hazard of pregnancy up to 210 d after first AI for all cows enrolled (hazard ratio = 1.04, 95% CI 0.90 to 1.19) and for cows that received treatments only (D32R = 308, AIER = 349; hazard ratio = 1.00, 95% CI 0.85 to 1.19) did not differ. We conclude that a program aimed at increasing the proportion of cows reinseminated at detected estrus by treatment with PGF at 32 ± 3 d after AI may be an alternative strategy for dairy farms that prefer or need to inseminate more cows at detected estrus rather than by TAI.
本实验的目的是比较在第一次配种后 210 天怀孕的时间和未怀孕的奶牛比例，这些奶牛采用了一种促进发情后再配种的生殖管理方案（AIE）或一种促进定时人工授精（TAI）的方案进行管理。第一次配种后，泌乳荷斯坦奶牛按胎次分组，随机分为第 32 天同期发情（D32R；n=464）或发情后同期发情（AIER；n=512）。为了确定管理策略对时间和怀孕的影响，在第一次 AI 服务后 210 天的风险期内未怀孕的奶牛，在 AIER 和 D32R 中继续接受管理，直到怀孕或离开牛群。D32R 中的奶牛在 AI 后 32±3 天接受 GnRH 治疗（第一次治疗干预；FTI）。7 天后，当非怀孕奶牛的黄体（CL）≥15mm 时，通过直肠超声检查进行非怀孕诊断（PGF，56 小时后 GnRH，16 至 18 小时后 TAI），并且没有 CL 的奶牛（NoCL 奶牛）参加 PreG-Ovsynch 方案（GnRH，7 天后 GnRH，7 天后 PGF，56 小时后 GnRH，16 至 18 小时 TAI）进行 TAI。对于 AIER 治疗，在 AI 后 32±3 天通过直肠超声检查发现的 CL≥15mm 的非怀孕奶牛接受 PGF 诱导发情。在 7 天内未进行 AIE 的奶牛参加同期发情（GnRH，7 天后 PGF，56 小时后 GnRH，16 至 18 小时 TAI）。AIER 中 NoCL 组的奶牛参加 PreG-Ovsynch。发情的检测是基于发情行为迹象的视觉观察和尾巴涂漆的去除。二项数据采用逻辑回归分析，时间事件数据采用 Cox 比例回归分析。在 FTI 后，AIER 中更多的奶牛进行了 AIE（36.0%比 11.9%），并且在 FTI 后 7 天内，更多的奶牛进行了 AIE（25.0%比 D32R 的 4.8%）。68±3 天后 AI 的总体怀孕率没有差异（AIER=35.5%比 D32R=34.7%）。第一次 AI 后 210 天所有奶牛（危险比=1.04，95%CI0.90 至 1.19）和仅接受治疗的奶牛（D32R=308，AIER=349；危险比=1.00，95%CI0.85 至 1.19）的怀孕风险没有差异。我们得出结论，在 AI 后 32±3 天通过 PGF 治疗增加发情后再配种比例的方案，可能是一种替代策略，适用于那些更喜欢或需要在发情时为更多奶牛配种而不是定时 AI 的奶牛场。
