Silva E, Sterry R A, Kolb D, Mathialagan N, McGrath M F, Ballam J M, Fricke P M
Department of Dairy Science, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Dairy Sci. 2009 Aug;92(8):3643-50. doi: 10.3168/jds.2008-1704.
The objective of this study was to compare 2 strategies for resynchronization of ovulation based on nonpregnant diagnoses using transrectal ultrasonography or a pregnancy-associated glycoprotein (PAG) ELISA. Lactating Holstein cows (n = 1,038) were submitted for first postpartum timed artificial insemination (TAI) using a Presynch + Ovsynch protocol. After the initial breeding, cows were randomly assigned to initiate resynchronization 25 d (D25) or 32 d (D32) later. Pregnancy status of cows initiating Resynch 25 d after TAI was determined 27 d after TAI by using a PAG ELISA, whereas pregnancy status of cows initiating Resynch 32 d after TAI was determined 39 d after TAI using transrectal ultrasonography. Cows diagnosed as not pregnant continued the Resynch protocol by receiving an injection of PGF(2 alpha) 7 d after the initial GnRH injection and a second GnRH injection 54 h after the PGF(2 alpha) injection. Cows in both treatments were inseminated approximately 16 h after the second GnRH injection. Blood samples for analysis of progesterone (P(4)) were collected at the first GnRH injection of each Resynch protocol. Pregnancies per AI (P/AI) of nonpregnant cows initiating Resynch 25 vs. 32 d after first postpartum TAI did not differ 39 d after TAI and were 28.3 vs. 30.9% for D25 vs. D32 cows, respectively. Mean P(4) at the first GnRH injection of Resynch was greater for D32 than for D25 cows (3.67 +/- 0.22 vs. 2.83 +/- 0.22 ng/mL), indicating that the Resynch treatments were initiated at different stages of the estrous cycle. After blocking P(4) concentration into low (<1.0 ng/mL) or high (>or=1.0 ng/mL) classes, P(4) class was not found to affect P/AI 39 d after TAI. Early resynchronization was not found to affect P/AI 39 d after TAI; however, early resynchronization did decrease days between inseminations and the interval from the initial nonpregnant diagnosis to conception. Earlier detection of nonpregnant cows using the PAG ELISA in conjunction with a TAI resynchronization program may improve the rate at which cows become pregnant in a dairy herd compared with transrectal ultrasonography conducted at a later stage after TAI.
本研究的目的是比较基于经直肠超声检查未妊娠诊断或妊娠相关糖蛋白（PAG）酶联免疫吸附测定（ELISA）的两种排卵再同步化策略。泌乳荷斯坦奶牛（n = 1038头）采用预同步化+排卵同步化方案进行首次产后定时人工授精（TAI）。初次配种后，奶牛被随机分配在25天（D25）或32天（D32）后开始再同步化。TAI后25天开始再同步化的奶牛的妊娠状态在TAI后27天通过PAG ELISA测定，而TAI后32天开始再同步化的奶牛的妊娠状态在TAI后39天通过经直肠超声检查测定。被诊断未妊娠的奶牛在初次促性腺激素释放激素（GnRH）注射后7天接受一次前列腺素F2α（PGF2α）注射，并在PGF2α注射后54小时接受第二次GnRH注射，从而继续再同步化方案。两种处理的奶牛均在第二次GnRH注射后约16小时进行人工授精。在每个再同步化方案的首次GnRH注射时采集血样用于孕酮（P4）分析。初次产后TAI后25天与32天开始再同步化的未妊娠奶牛的每次人工授精妊娠率（P/AI）在TAI后39天无差异，D25组和D32组奶牛分别为28.3%和30.9%。再同步化首次GnRH注射时D32组奶牛的平均P4高于D25组奶牛（3.67±0.22对2.83±0.22 ng/mL），表明再同步化处理在发情周期的不同阶段开始。将P4浓度分为低（<1.0 ng/mL）或高（≥1.0 ng/mL）类别后，发现P4类别不影响TAI后39天的P/AI。未发现早期再同步化影响TAI后39天的P/AI；然而，早期再同步化确实减少了两次人工授精之间的天数以及从初次未妊娠诊断到受孕的间隔时间。与TAI后期进行的经直肠超声检查相比，在TAI再同步化方案中结合使用PAG ELISA更早地检测未妊娠奶牛可能会提高奶牛场中奶牛的受孕率。
