Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland.
J Dairy Sci. 2011 Sep;94(9):4488-501. doi: 10.3168/jds.2010-4126.
Lactating dairy cows (n=1,538) were enrolled in a randomized complete block design study to evaluate protocols to synchronize estrus and ovulation. Within each herd (n=8), cows were divided into 3 calving groups: early, mid, and late, based on days in milk (DIM) at mating start date (MSD). Early calving cows (n=1,244) were ≥42 DIM at MSD, mid-calving cows (n=179) were 21 to 41 DIM at MSD, and late-calving cows (n=115) were 0 to 20 DIM at MSD. Cows in the early, mid-, and late-calving groups were synchronized to facilitate estrus or timed AI (TAI) at MSD (planned breeding 1; PB1), 21 d (PB2), and 42 d (PB3) after MSD, respectively. For each PB, cows in the relevant calving group were stratified by parity and calving date and randomly assigned to 1 of 4 experimental groups: (1) d -10 GnRH (10 μg of i.m. buserelin) and controlled internal drug release insert (CIDR; 1.38 g of progesterone); d -3 PGF(2α) (25 mg of i.m. dinoprost); and d -2 CIDR out and AI at observed estrus (CIDR_OBS); (2) same as CIDR_OBS, but GnRH 36 h after CIDR out and TAI 18 h later (CIDR_TAI); (3) same as CIDR_TAI, but no CIDR (Ovsynch); or (4) untreated controls (CTRL). The CIDR_OBS, CIDR_TAI, and Ovsynch had shorter mean intervals from calving to first service compared with the CTRL (69.2, 63.4, and 63.7 vs. 73.7 d, respectively). Both CIDR_OBS (predicted probability; PP of pregnancy=0.59) and CIDR_TAI (PP of pregnancy=0.54) had increased odds of conceiving at first service compared with Ovsynch [PP of pregnancy=0.45; odds ratio (OR)=1.81 and OR=1.46, respectively], and Ovsynch had decreased likelihood of conceiving at first service (OR=0.70) compared with CTRL (PP of pregnancy=0.53). Both CIDR_TAI hazard ratio; HR [95% confidence interval=1.21 (1.04, 1.41)] and Ovsynch [HR (95% confidence interval)=1.23 (1.05, 1.44)] were associated with an increased likelihood of earlier conception compared with the CTRL. A greater proportion of cows on the CIDR_TAI treatment successfully established pregnancy in the first 42 d of the breeding season compared with the CTRL (0.75 vs. 0.67 PP of 42-d pregnancy, respectively). Protocols to synchronize estrus and ovulation were effective at achieving earlier first service and conception in pasture-based seasonal calving dairy herds. However, animals that conceived following insemination at observed estrus had a decreased likelihood of embryo loss to first service compared with animals bred with TAI (PP of embryo loss after first service=0.05 vs. 0.09; OR=0.52).
哺乳期奶牛（n=1538）被纳入一项随机完全分组设计研究中，以评估同步发情和排卵的方案。在每个牛群（n=8）内，根据配种开始日期（MSD）时的产奶天数（DIM），将奶牛分为 3 个产犊组：早期、中期和晚期。早期产犊奶牛（n=1244）在 MSD 时的 DIM 大于 42 天，中期产犊奶牛（n=179）在 MSD 时的 DIM 为 21 至 41 天，晚期产犊奶牛（n=115）在 MSD 时的 DIM 为 0 至 20 天。早期、中期和晚期产犊组的奶牛被同步发情或定时人工授精（TAI），分别在 MSD（计划配种 1；PB1）、21 天（PB2）和 42 天（PB3）后进行。对于每个 PB，相关产犊组的奶牛按胎次和产犊日期分层，并随机分配到 4 个实验组中的 1 个：（1）-10 天 GnRH（10 μg 肌肉内注射布舍瑞林）和控释宫内药物释放插入物（CIDR；1.38 g 孕酮）；-3 天 PGF(2α)（25 mg 肌肉内注射地诺前列酮）；-2 天 CIDR 取出和发情观察时授精（CIDR_OBS）；（2）与 CIDR_OBS 相同，但 CIDR 取出后 36 小时给予 GnRH 和 18 小时后进行 TAI（CIDR_TAI）；（3）与 CIDR_TAI 相同，但不使用 CIDR（Ovsynch）；或（4）未处理的对照组（CTRL）。与 CTRL 相比，CIDR_OBS、CIDR_TAI 和 Ovsynch 从产犊到第一次配种的平均间隔更短（分别为 69.2、63.4 和 63.7 天）。与 Ovsynch 相比，CIDR_OBS（预测概率；妊娠率为 0.59）和 CIDR_TAI（妊娠率为 0.54）的首次配种妊娠率更高[妊娠率为 0.45；优势比（OR）分别为 1.81 和 1.46]，而 Ovsynch 的首次配种妊娠率降低（OR=0.70）与 CTRL 相比（妊娠率为 0.53）。CIDR_TAI 危险比（HR）[95%置信区间为 1.21（1.04，1.41）]和 Ovsynch [HR（95%置信区间为 1.23（1.05，1.44）]与 CTRL 相比，首次妊娠的可能性增加。与 CTRL 相比，CIDR_TAI 治疗组中更多的奶牛在繁殖季节的前 42 天内成功建立了妊娠（0.75 对 0.67 的 42 天妊娠率，分别）。同步发情和排卵的方案可有效提高牧场季节性产犊奶牛的首次配种和妊娠时间。然而，与 TAI 配种的奶牛相比，发情观察时授精后怀孕的奶牛胚胎丢失的可能性降低（首次配种后的胚胎丢失率为 0.05 对 0.09；OR=0.52）。
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