The Extent and Timing of Embryonic Mortality in the Cow

Abstract

The extent and timing of embryonic mortality in heifers, normal cows and repeat breeder cows has been reviewed. Average fertilisation rates for normal heifers and cows were 88 and 90 percent while calving rate to a single service averaged 55 percent overall. Based on a fertilisation rate of 89 percent this is equivalent to a total level of embryonic mortality of the order of 39 percent. In normal cows, embryonic mortality of the order of 38 percent. In normal cows, embryonic mortality would seem to occur gradually after fertilisation but with the greatest increment of loss occurring between about Days 15 to 18. Embryo losses after implantation through to full term are of the order of 5 to 8 percent. Reports on the extent and timing of embryonic mortality in repeat breeder cows are inconsistent. The unilateral or bilateral distribution of two embryos within the uterus had no effect on subsequent embryo or foetal mortality.