Fricke P M, Carvalho P D, Lucy M C, Curran F, Herlihy M M, Waters S M, Larkin J A, Crowe M A, Butler S T
Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
Department of Dairy Science, University of Wisconsin-Madison, Madison 53706.
J Dairy Sci. 2016 Aug;99(8):6780-6792. doi: 10.3168/jds.2016-11229. Epub 2016 Jun 16.
Fertility to timed AI (TAI) is profoundly affected by progesterone (P4) levels during hormonal synchronization protocols. Holstein-Friesian dairy cows managed in a seasonal-calving, pasture-based production system were randomly assigned to 2 treatments to manipulate P4 before TAI during growth of the preovulatory follicle. Cows in the first treatment (High P4; n=30) were submitted to a Double-Ovsynch protocol {Pre-Ovsynch [GnRH; 7 d, PGF2α; 3 d, GnRH] followed 7 d later by Breeding-Ovsynch [GnRH (G1); 7 d PGF2α; 24 h, PGF2α; 32 h, GnRH (G2); 16 h, TAI]}. Cows in the second treatment (n=30; Low P4) received the same Double-Ovsynch protocol but with an additional PGF2α treatment 24 h after G1. Overall, synchronization rate did not differ between treatments and was 92% (55/60). Unexpectedly, 37% of Low P4 cows were detected in estrus ~24 h before scheduled TAI and were inseminated ~16 h before scheduled TAI. Overall, P4 did not differ between treatments at G1, whereas High P4 cows had greater P4 concentrations at PGF2α and G2 than Low P4 cows. High P4 cows had the smallest mean follicle diameter at G2, whereas Low P4 cows with no estrus before TAI had intermediate mean follicle diameter at G2, and Low P4 cows with estrus before TAI had the largest mean follicle diameter. Low P4 cows with estrus before TAI had larger corpora lutea 15 d after TAI than Low P4 cows without estrus before TAI or High P4 cows. In accordance with corpus luteum size on d 15, High P4 cows and Low P4 cows without estrus before TAI had lower P4 from 4 to 46 d after TAI than Low P4 cows with estrus before TAI. Relative mRNA levels of the interferon-stimulated genes ISG15, MX1, MX2, and OAS1 were greater for Low P4 than for High P4 cows, whereas relative mRNA levels of RTP4 were greater for High P4 than for Low P4 cows 18 d after TAI. Treatment did not affect plasma pregnancy-associated glycoprotein concentrations after TAI; however, pregnancy-associated glycoprotein concentrations were affected by pregnancy status and parity. Treatment did not affect pregnancy per artificial insemination at 29, 39, or 60 d after TAI, and no pregnancy losses were observed from 39 to 60 d after TAI. We concluded that (1) Low P4 cows were more likely to express estrus than High P4 cows; (2) the subpopulation of Low P4 cows that expressed estrus had larger preovulatory follicles and greater P4 concentrations after TAI; and (3) regardless of estrus before TAI, all Low P4 cows had greater mRNA expression for 5 of 6 interferon-stimulated genes than High P4 cows 18 d after TAI.
在激素同步方案期间，定时人工授精（TAI）的受胎率会受到孕酮（P4）水平的深刻影响。在季节性产犊、以牧场为基础的生产系统中管理的荷斯坦-弗里生奶牛被随机分配到2种处理中，以在排卵前卵泡生长期间的TAI之前操纵P4。第一种处理（高P4；n = 30）的奶牛接受双同期发情方案{预同期发情[促性腺激素释放激素（GnRH）；7天，前列腺素F2α（PGF2α）；3天，GnRH]，7天后接着进行配种同期发情[GnRH（G1）；7天，PGF2α；24小时，PGF2α；32小时，GnRH（G2）；16小时，TAI]}。第二种处理（n = 30；低P4）的奶牛接受相同的双同期发情方案，但在G1后24小时额外进行一次PGF2α处理。总体而言，处理之间的同步率没有差异，为92%（55/60）。出乎意料的是，37%的低P4奶牛在预定TAI前约24小时被检测到发情，并在预定TAI前约16小时进行了授精。总体而言，在G1时处理之间的P4没有差异，而高P4奶牛在PGF2α和G2时的P4浓度高于低P4奶牛。高P4奶牛在G2时的平均卵泡直径最小，而在TAI前未发情的低P4奶牛在G2时的平均卵泡直径中等，在TAI前发情的低P4奶牛的平均卵泡直径最大。在TAI后15天，在TAI前发情的低P4奶牛的黄体比在TAI前未发情的低P4奶牛或高P4奶牛更大。根据第15天的黄体大小，高P4奶牛和在TAI前未发情的低P4奶牛在TAI后4至46天的P4低于在TAI前发情的低P4奶牛。低P4奶牛的干扰素刺激基因ISG15、MX1、MX2和OAS1的相对mRNA水平高于高P4奶牛，而在TAI后18天，高P4奶牛的RTP4相对mRNA水平高于低P4奶牛。处理对TAI后的血浆妊娠相关糖蛋白浓度没有影响；然而，妊娠相关糖蛋白浓度受妊娠状态和胎次的影响。处理对TAI后29、39或60天的每次人工授精妊娠率没有影响，并且在TAI后39至60天未观察到妊娠损失。我们得出结论：（1）低P4奶牛比高P4奶牛更有可能表现出发情；（2）表现出发情的低P4奶牛亚群在TAI后有更大的排卵前卵泡和更高的P4浓度；（3）无论在TAI前是否发情，所有低P4奶牛在TAI后18天的6种干扰素刺激基因中的5种的mRNA表达都高于高P4奶牛。
