Saacke R G
Virginia Polytechnic Institute and State University, Department of Dairy Science, Blacksburg, VA 24061 0315, United States.
Theriogenology. 2008 Aug;70(3):479-84. doi: 10.1016/j.theriogenology.2008.04.015. Epub 2008 May 22.
Six-day-old bovine ova/embryos were recovered non-surgically and used as biomonitors to evaluate time of artificial insemination. These embryos/ova provided information regarding fertilization status and embryo quality, as well as quantitative and qualitative data regarding associated accessory sperm. Both sperm access to the ovum (addressed by accessory sperm) and fertilization status/embryo quality were important in addressing pregnancy rate for specific intervals from the onset of estrus to insemination. Based on these biomonitors, early insemination failed to achieve optimum pregnancy rate due to inadequate access of sperm to the ovum (i.e., low fertilization rate, manifested by low accessory sperm numbers). However, embryo quality was high in early inseminations, which favors pregnancy. Late insemination failed to achieve optimum pregnancy rate (due to reduced embryo quality), however, sperm access to the ovum was highest. Thus, the selection of an insemination time to achieve optimum pregnancy rate appeared to be a compromise between the two extreme intervals. For timed-AI programs, consideration of the time of ovulation (and its variability) becomes important, in addition to conventional considerations, such as semen handling, site of insemination, and bull selection.
6日龄的牛卵子/胚胎通过非手术方式采集，并用作生物监测指标以评估人工授精时间。这些胚胎/卵子提供了有关受精状态和胚胎质量的信息，以及有关相关附属精子的定量和定性数据。精子与卵子的接触（由附属精子体现）以及受精状态/胚胎质量对于确定从发情开始到授精的特定时间段内的妊娠率都很重要。基于这些生物监测指标，早期授精由于精子与卵子的接触不足（即受精率低，表现为附属精子数量少）而未能达到最佳妊娠率。然而，早期授精时胚胎质量较高，这有利于妊娠。晚期授精也未能达到最佳妊娠率（由于胚胎质量下降），不过精子与卵子的接触最为充分。因此，选择能达到最佳妊娠率的授精时间似乎是在这两个极端时间段之间进行的一种权衡。对于定时人工授精程序，除了精液处理、授精部位和公牛选择等常规考虑因素外，考虑排卵时间（及其变异性）也变得很重要。
