Giordano J O, Stangaferro M L, Wijma R, Chandler W C, Watters R D
Department of Animal Science, Cornell University, Ithaca, NY 14853.
Department of Animal Science, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 2015 Apr;98(4):2488-501. doi: 10.3168/jds.2014-8961. Epub 2015 Feb 7.
The objective of this study was to compare the reproductive performance of lactating dairy cows using a treatment (TRT) program for second and subsequent artificial insemination (AI) services aimed at (1) increasing AI upon estrus detection based on increased physical activity (AIAct) and (2) increasing fertility of timed AI (TAI) services for cows not AIAct through presynchronization of the estrous cycle and improved physiological milieu before TAI. Cows in the control (CON) group were managed with a program that combined AIAct and TAI after the Ovsynch protocol. After nonpregnancy diagnosis (NPD) by transrectal ultrasonography at 31 ± 3 d after AI, cows received the following treatments: (1) CON (n=634), AIAct any time after a previous AI and resynchronization with the Ovsynch-56 protocol (GnRH-7d-PGF2α-56 h-GnRH-16 h-TAI) 1d after NPD, or (2) TRT (n = 616): cows with a corpus luteum (CL) ≥ 20 mm (TRT-CL) received a PGF2α injection 1d after NPD, whereas cows with no CL or a CL < 20 mm (TRT-NoCL) received a GnRH injection 3d after NPD. Cows in TRT-CL and TRT-NoCL not AIAct were enrolled in a 5-d Ovsynch + progesterone protocol (GnRH + controlled internal drug release-5d-PGF2α + controlled internal drug release removal-24 h-PGF2α -32 h-GnRH-16 h-TAI) 9 and 7d after the PGF2α or GnRH injection, respectively, to receive TAI. The hazard of pregnancy up to 270 DIM was similar for cows in the CON and TRT group (hazard ratio = 1.07, 95% CI = 0.95 to 1.21), but it was affected by parity (primiparous greater than multiparous cows). Median days to pregnancy for the CON and TRT group were 111 and 110 d, respectively. When evaluated after 104 DIM (first time point at which cows were affected by the treatments), the hazard of pregnancy was similar for the CON and TRT group (hazard ratio = 1.15, 95% CI = 0.95 to 1.39). Based on this analysis, median days to pregnancy for the CON and TRT group were 161 and 178 d, respectively. Thus, in spite of increasing the proportion of cows AIAct (29 and 10% for TRT and CON), median days to insemination after NPD were greater for cows in the TRT (17 d) than the CON (10 d) group, which coupled with similar fertility to AIAct, and TAI failed to improve overall reproductive performance. A low proportion of cows with a CL at NPD (65.2%) and a poor response to PGF2α may explain the poor estrus detection efficiency in the TRT group. We concluded that, when compared with a typical estrus detection and TAI program for cows failing to conceive to previous AI services, a program aimed at increasing the proportion of cows AIAct after NPD and fertility of TAI services increased the proportion of cows AIAct but failed to reduce days to pregnancy during lactation because of greater days to AI after NPD.
本研究的目的是比较泌乳奶牛的繁殖性能，采用一种针对第二次及后续人工授精（AI）服务的处理（TRT）方案，该方案旨在：（1）基于增加的身体活动在发情检测时增加人工授精（AIAct），以及（2）通过发情周期的预同步和在定时人工授精（TAI）前改善生理环境，提高未进行AIAct的奶牛定时人工授精（TAI）服务的受胎率。对照组（CON）的奶牛采用在Ovsynch方案后结合AIAct和TAI的方案进行管理。在人工授精后31±3天通过经直肠超声进行非妊娠诊断（NPD）后，奶牛接受以下处理：（1）CON组（n = 634），在先前人工授精后的任何时间进行AIAct，并在NPD后1天与Ovsynch - 5,6方案（GnRH - 7天 - PGF2α - 56小时 - GnRH - 16小时 - TAI）重新同步；或（2）TRT组（n = 616）：黄体（CL）≥20 mm的奶牛（TRT - CL）在NPD后1天接受PGF2α注射，而无CL或CL < 20 mm的奶牛（TRT - NoCL）在NPD后3天接受GnRH注射。TRT - CL组和TRT - NoCL组中未进行AIAct的奶牛分别在PGF2α或GnRH注射后9天和7天参加为期5天的Ovsynch +孕酮方案（GnRH +控释内投药 - 5天 - PGF2α +控释内投药去除 - 24小时 - PGF2α - 32小时 - GnRH - 16小时 - TAI）以接受TAI。CON组和TRT组奶牛直至270天产犊间隔（DIM）的妊娠风险相似（风险比 = 1.07，95%置信区间 = 0.95至1.21），但受胎次影响（初产奶牛大于经产奶牛）。CON组和TRT组的妊娠中位数天数分别为111天和110天。在104 DIM后评估时（奶牛受处理影响的第一个时间点），CON组和TRT组的妊娠风险相似（风险比 = 1.15，95%置信区间 = 0.95至1.39）。基于此分析，CON组和TRT组的妊娠中位数天数分别为161天和178天。因此，尽管TRT组和CON组中进行AIAct的奶牛比例增加（分别为29%和10%），但TRT组奶牛在NPD后的人工授精中位数天数（17天）比CON组（10天）更长，这与AIAct和TAI的相似受胎率相结合，未能改善整体繁殖性能。NPD时黄体奶牛比例较低（65.2%）以及对PGF2α反应不佳可能解释了TRT组中发情检测效率低下的原因。我们得出结论，与针对先前人工授精服务未受孕奶牛的典型发情检测和TAI方案相比，旨在增加NPD后进行AIAct的奶牛比例和TAI服务受胎率的方案增加了进行AIAct的奶牛比例，但由于NPD后至人工授精的天数增加，未能缩短泌乳期的妊娠天数。
