Influence of the period from thawing to transfer of embryos and trucking of recipients on pregnancy rates in bovine embryo transfer

The present study was designed to investigate the influence of the period from thawing of frozen bovine compacted morula embryos to non-surgical transfer to recipients and of transportation of the recipients (by truck) to our Embryo Transfer Institute on pregnancy rates. In Experiment 1, excellent or good compacted morula embryos were aspirated into a straw for transfer 16 - 17 minutes after the initiation of thawing. The embryos were transported to the breeding farm and transferred to the recipients consisting of 96 nulliparous Holstein heifers, 105 Japanese Black cows, and 35 cross breeds. Pregnancy rates were determined at 11 - 20 (Group 1), 21 - 30 (Group 2), 31 - 40 (Group 3), 41 - 50 (Group 4) and 51 - 60 minutes (Group 5) after aspiration into the straw. The rates were 50.0% (2/4) to 73.7% (14/19) in Groups 1 through 5 of the Holstein heifers, 50.0% (3/6) to 62.5% (20/32) in Groups 2 through 5 of the Japanese Black cows, and 43.8% (7/16) to 60.0% (6/10) in Groups 2 to 4 of the cross breeds (Japanese Black strain x Holstein strain). No significant differences were found among the groups. In Experiment 2, the Holstein heifer recipients were transported from the breeding farm to our Embryo Transfer Institute by truck which took 1.4 - 1.6 hours (58 - 62 kilometers one way). After transportation the recipients were maintained in stalls for approximately 20 minutes until thawing of the frozen embryos and aspiration of the thawed embryos into the straw were completed. Then procedures similar to those for Experiment 1 were conducted; the embryos were transferred within 10 minutes (Group 6) and 11 - 20 minutes (Group 7) after the aspiration. The pregnancy rates of the recipients transported by truck, receiving embryo transfer within 30 minutes after aspiration, were determined. They were 69.7% (23/33) and 66.7% (6/9) in Groups 6 and 7, respectively, with no significant difference