Eggs were transferred surgically from fifty-three donor heifers to ninety-nine recipients which were allocated to different groups according to the degree of synchronization of oestrus between donor and recipient.The pregnancy rate obtained was 0%, 30%, 52\m=.\2%,91\m=.\1%,56\m=.\5%, 40% and 20% where the degree of synchronization of the recipient in relation to the donor was \m=-\3,\m=-\2, \m=-\ 1, 0, + 1, +2, +3 days, respectively. Storage of eggs for periods of up to 6 hr did not influence the pregnancy rate.The high pregnancy rate obtained where synchronization was exact may have been due to the rejection of retarded or abnormal eggs before transfer.It is concluded that the synchronization requirements for successful egg transfer in the cow are slightly more acute than in the sheep and should not vary by more than \m=+-\1day.

This study examines two descriptive parameters of embryo morphology to determine if either parameter correlates with subsequent pregnancy rates (PRs). The two parameters were the evenness (similarity in size) of the blas-tomeres and the degree of cellular fragmentation. A total of 242 embryo transfers in which 4 embryos were transferred were included. Sixty-nine (28.5%) clinical and 62 (25.6%) viable pregnancies resulted. In all cases 4 embryos were transferred, but the number of embryos with even round blastomeres (grade 1) varied from 0 to 4. Statistically, there was no correlation between PR and number of grade 1 embryos transferred. When 4 grade 1 embryos were transferred, the PR was 33.3 versus 28.1% when no grade 1 embryos were transferred. There was, however, a statistical difference in the implantation rate; a higher frequency of multiple gestations occurred when 3 or 4 of the embryos transferred were graded 1:12.7 as compared with 6.7% when < 2 embryos were grade 1. The significance of the degree of cellular fragmentation in the embryos was also assessed. There was no statistical difference in the PR according to the number (0–4) of embryos transferred that did not have fragments (grade A). When 4 grade A embryos were transferred, the PR was 18.2 versus 26.1 % when there were no grade A embryos. Neither implantation nor multiple-birth rates correlated with fragmentation.

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