Egg Transfer in the Cow: Synchronization Requirements

Summary. 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%, 52·2%, 91·1%, 56·5%, 40% and 20% where the degree of synchronization of the recipient in relation to the donor was −3, −2, −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 ±1 day.