Sterry R A, Welle M L, Fricke P M
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
J Dairy Sci. 2006 Jun;89(6):2099-109. doi: 10.3168/jds.S0022-0302(06)72280-9.
To compare 2 strategies for systematically resynchronizing ovulation, lactating Holstein cows (n = 763) at various days in milk and prior artificial insemination services were assigned randomly at timed AI (TAI) to receive the first GnRH injection of Ovsynch 26 (D26) or 33 (D33) d after TAI to resynchronize ovulation (Resynch) in cows failing to conceive. Cows in the D26 treatment received GnRH 26 d after TAI and continued Resynch only when diagnosed not pregnant by using ultrasonography 33 d after TAI, whereas D33 cows initiated Resynch only when diagnosed not pregnant 33 d after TAI. Cows were classified based on the presence or absence of a corpus luteum (CL) at the not-pregnant diagnosis, and cows without a CL received an intravaginal progesterone-releasing insert during Resynch. When analyzed as a systematic strategy, pregnancy rate per AI (PR/AI) was greater for cows assigned to the D33 than the D26 Resynch treatment (39.4 vs. 28.6%). A treatment x parity interaction was detected for PR/AI after Resynch for nonpregnant cows having a CL in which primiparous cows had a greater PR/AI than multiparous cows when Resynch was initiated 33 d after the initial TAI, and primiparous and multiparous cows when Resynch was initiated 26 d after the initial TAI. Pregnancy loss for Resynch was 6.4% between 33 and 40 d, and 2.6% between 40 and 61 d after Resynch TAI. We concluded that delaying initiation of Resynch until 33 d after TAI increased PR/AI for primiparous cows.
为比较两种系统性重新同步排卵的策略，将处于不同泌乳天数且先前接受过人工授精的763头泌乳荷斯坦奶牛在定时人工授精（TAI）时随机分配，在TAI后26天（D26）或33天（D33）接受第一次促性腺激素释放激素（GnRH）注射，以对未受孕奶牛的排卵进行重新同步（再同步）。D26处理组的奶牛在TAI后26天接受GnRH注射，只有在TAI后33天经超声检查诊断未怀孕时才继续进行再同步，而D33组奶牛只有在TAI后33天诊断未怀孕时才开始再同步。根据未怀孕诊断时黄体（CL）的有无对奶牛进行分类，无CL的奶牛在再同步期间接受阴道内孕激素释放装置。作为一种系统性策略进行分析时，分配到D33再同步处理组的奶牛每人工授精的妊娠率（PR/AI）高于D26组（39.4%对28.6%）。对于再同步后未怀孕且有CL的奶牛，检测到处理×胎次交互作用，即当初始TAI后33天开始再同步时，初产奶牛的PR/AI高于经产奶牛；当初始TAI后26天开始再同步时，初产奶牛和经产奶牛的PR/AI情况。再同步后的妊娠损失在再同步TAI后33至40天为6.4%，40至61天为2.6%。我们得出结论，将再同步的开始时间推迟到TAI后33天可提高初产奶牛的PR/AI。
