Effects of the Age of Donor Embryos on the Developmental Ability of Bovine Nuclear Transferred Eggs In Vitro.

The effect of the age of a donor embryo on the developmental ability of bovine nuclear transferred eggs was examined. A blastomere of an in vitro fertilized embryo cultured for 3.5 to 6.5 days, or an inner cell mass cell (ICM) from a blastocyst cultured for 7.5 days was fused with an enucleated, preactivated oocyte matured in vitro by electrical stimulation. Fused eggs were co-cultured with cumulus cells for 10 days in vitro. The fusion rate of blastomeres from day 3.5 to 6.5 embryos with enucleated oocytes (78 to 88%) and the developmental ability of nuclear transferred eggs to blastocysts (6 to 10%) were not significantly affected by the age of the donor embryo. However, the fusion rate of the ICM cell was significantly low (28%). Although nuclear transferred eggs receiving an ICM cell developed to 2-cell (73%) and 8-cell (22%) stages at the same rates as those obtained in other groups (68 to 81% for 2-cell, 30 to 34% for 8-cell), none of them developed to blastocysts.