The viability of early cleavage stages containing half the normal number of blastomeres in the sheep

Abstract

The developmental capacity of embryos produced by injection of single blastomeres of 2 cell embryos, pairs of blastomeres of 4 cell embryos or 4 blastomeres of 8 cell embryos into foreign zonae pellucidae was studied. The micromanipulated embryos were embedded in tiny agar cylinders, transferred to ligated oviducts of ewes on days 2-8 of their estrous cycle and recovered when the total age of the embryos was 5 1/2-6 1/2 days. Of 78 embryos transferred, 69 (88.5%) were recovered and of the latter 65 (94.2%) had developed at a normal rate. Of these half embryos 30 were transferred to ewes on day 6 of the estrous cycle: 24 (80%) developed into lambs. There were no apparent differences between embryos derived from the 2, 4 or 8 cell embryos with respect to developmental capacity. A further 12 half embryos were stored by deep-freezing for 1 or 2 mo. After thawing, 9 of these were selected for transfer to ewes on day 6: 3 developed into lambs, each of which was the monozygotic twin of a lamb resulting from the 1st series of transfers.