Effect of the donor on egg quality and transfer results

Embryo transfer with high-producing animals as donors led to new problems. Optimal results depended on a strict preselection of donors. Animals with a) a critical anamnesis, b) a calving-superovulation interval of more than 90 days, or c) from herds with decreased fertility should be carefully evaluated prior to superovulation and embryo transfer. The advantage of preselected donors is that the proportion of morphologically damaged embryos is less and therefore the chance of misjudging embryo quality is lower. Even if the preselection of donors is possible, the use of high producing cows with critical anamnesis cannot be avoided in certain cases, especially if the owner wants to use such animals. A better selection of embryo viability might occur naturally if the embryos were recovered on days 10 to 12 instead of on day 7. However, the uterine conditions for embryonic survival worsen steadily after day 4. This embryonic loss cannot be tolerated, especially in very valuable cows. Also, tranfer results of 75 p. 100 or higher could apparently not be obtained with older embryos. The problems discussed force us to search for criteria other than morphological appearance for judging the viability of day 7 embryos.