Diskin M G, Waters S M, Parr M H, Kenny D A
Teagasc, Animal and Grassland and Innovation Research Centre, Mellows Campus, Athenry, Co. Galway, H65 R718, Ireland.
Teagasc, Animal and Grassland and Innovation Research Centre, Grange, Dunsany, Co. Meath, C15 PW93, Ireland.
Reprod Fertil Dev. 2016;28(1-2):83-93. doi: 10.1071/RD15366.
For heifers, beef and moderate-yielding dairy cows, it appears that the fertilisation rate generally lies between 90% and 100%. For high-producing dairy cows, there is a less substantive body of literature, but it would appear that the fertilisation rate is somewhat lower and possibly more variable. In cattle, the major component of embryo loss occurs in the first 16 days following breeding (Day 0), with emerging evidence of greater losses before Day 8 in high-producing dairy cows. In cattle, late embryo mortality causes serious economic losses because it is often recognised too late to rebreed females. Systemic concentrations of progesterone during both the cycle preceding and following insemination affect embryo survival, with evidence of either excessive or insufficient concentrations being negatively associated with survival rate. The application of direct progesterone supplementation or treatments to increase endogenous output of progesterone to increase embryo survival cannot be recommended at this time. Energy balance and dry matter intake during the first 4 weeks after calving are critically important in determining pregnancies per AI when cows are inseminated at 70-100 days after calving. Level of concentrate supplementation of cows at pasture during the breeding period has minimal effects on conception rates, although sudden reductions in dietary intake should be avoided. For all systems of milk production, more balanced breeding strategies with greater emphasis on fertility and feed intake and/or energy must be developed. There is genetic variability within the Holstein breed for fertility traits, which can be exploited. Genomic technology will not only provide scientists with an improved understanding of the underlying biological processes involved in fertilisation and the establishment of pregnancy, but also, in the future, could identify genes responsible for improved embryo survival. Such information could be incorporated into breeding objectives in order to increase the rate of genetic progress for embryo survival. In addition, there is a range of easily adoptable management factors, under producer control, that can either directly increase embryo survival or ameliorate the consequences of low embryo survival rates. The correction of minor deficits in several areas can have a substantial cumulative positive effect on herd reproductive performance.
对于小母牛、肉牛和中产奶牛而言，受精率通常似乎在90%至100%之间。对于高产奶牛，相关文献较少，但受精率似乎略低且可能更具变异性。在牛群中，胚胎损失的主要部分发生在配种后的前16天（第0天），越来越多的证据表明，高产奶牛在第8天之前的损失更大。在牛群中，晚期胚胎死亡会造成严重的经济损失，因为往往发现太晚而无法让母牛再次配种。授精前后周期内孕酮的全身浓度会影响胚胎存活，有证据表明，浓度过高或过低都与存活率呈负相关。目前不建议应用直接补充孕酮或进行处理以增加孕酮的内源性分泌来提高胚胎存活率。当奶牛在产犊后70 - 100天进行授精时，产犊后前4周的能量平衡和干物质摄入量对于确定每次人工授精的妊娠率至关重要。在繁殖期，给放牧奶牛补充精料的水平对受孕率影响极小，不过应避免日粮摄入量突然减少。对于所有牛奶生产系统，必须制定更平衡的繁殖策略，更加注重繁殖力以及采食量和/或能量。荷斯坦品种内存在繁殖力性状的遗传变异性，可加以利用。基因组技术不仅将使科学家更好地理解受精和妊娠建立所涉及的潜在生物学过程，而且在未来还能够识别出有助于提高胚胎存活率的基因。此类信息可纳入育种目标，以提高胚胎存活率的遗传进展速度。此外，在生产者可控的范围内，有一系列易于采用的管理因素，它们要么能直接提高胚胎存活率，要么能减轻胚胎存活率低的后果。纠正几个方面的微小不足会对牛群繁殖性能产生显著的累积积极影响。
