Department of Animal & Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA.
J Anim Sci. 2019 May 30;97(6):2555-2568. doi: 10.1093/jas/skz116.
In vitro embryo production (IVP) in cattle has gained worldwide interest in recent years, but the efficiency of using IVP embryos for calf production is far from optimal. This review will examine the pregnancy retention rates of IVP embryos and explore causes for pregnancy failures. Based on work completed over the past 25 yr, only 27% of cattle receiving IVP embryos will produce a live calf. Approximately 60% of these pregnancies fail during the first 6 wk of gestation. When compared with embryos generated by superovulation, pregnancy rates are 10% to 40% lower for cattle carrying IVP embryos, exemplifying that IVP embryos are consistently less competent than in vivo-generated embryos. Several abnormalities have been observed in the morphology of IVP conceptuses. After transfer, IVP embryos are less likely to undergo conceptus elongation, have reduced embryonic disk diameter, and have compromised yolk sac development. Marginal binucleate cell development, cotyledon development, and placental vascularization have also been documented, and these abnormalities are associated with altered fetal growth trajectories. Additionally, in vitro culture conditions increase the risk of large offspring syndrome. Further work is needed to decipher how the embryo culture environment alters post-transfer embryo development and survival. The risk of these neonatal disorders has been reduced by the use of serum-free synthetic oviductal fluid media formations and culture in low oxygen tension. However, alterations are still evident in IVP oocyte and embryo transcript abundances, timing of embryonic cleavage events and blastulation, incidence of aneuploidy, and embryonic methylation status. The inclusion of oviductal and uterine-derived embryokines in culture media is being examined as one way to improve the competency of IVP embryos. To conclude, the evidence presented herein clearly shows that bovine IVP systems still must be refined to make it an economical technology in cattle production systems. However, the current shortcomings do not negate its current value for certain embryo production needs and for investigating early embryonic development in cattle.
近年来，体外胚胎生产（IVP）在牛中引起了广泛关注，但利用 IVP 胚胎生产小牛的效率远非最佳。本综述将检查 IVP 胚胎的妊娠保留率，并探讨妊娠失败的原因。基于过去 25 年完成的工作，只有 27%接受 IVP 胚胎的牛会生产活牛犊。这些妊娠中约有 60%在妊娠的前 6 周失败。与超数排卵产生的胚胎相比，携带 IVP 胚胎的牛的妊娠率低 10%至 40%，这表明 IVP 胚胎的活力始终低于体内产生的胚胎。在形态学上，已经观察到 IVP 胚胎存在几种异常。移植后，IVP 胚胎不太可能进行胚胎伸长，胚胎盘直径减小，卵黄囊发育受损。也记录了边缘双核细胞发育、胎叶发育和胎盘血管化，这些异常与胎儿生长轨迹的改变有关。此外，体外培养条件增加了发生巨大儿综合征的风险。需要进一步的工作来阐明胚胎培养环境如何改变胚胎移植后的发育和生存。通过使用无血清合成输卵管液培养基和在低氧张力下培养，可以降低这些新生儿疾病的风险。然而，IVP 卵母细胞和胚胎转录物丰度、胚胎分裂事件和囊胚形成的时间、非整倍体的发生率以及胚胎甲基化状态的改变仍然存在。在培养物中添加输卵管和子宫衍生的胚胎细胞因子，被认为是提高 IVP 胚胎活力的一种方法。总之，本文提供的证据清楚地表明，牛的 IVP 系统仍需进一步改进，使其成为牛生产系统中的一种经济技术。然而，目前的缺点并不能否定其在某些胚胎生产需求和研究牛早期胚胎发育方面的当前价值。
