Effect of morphological properties of transferred embryonic stages on tubal migration Implications for in vivo culture in the bovine oviduct.

In cattle, there is no practical method, which allows tubal transfer of pre-implantation embryos for routine in vivo culture as it has been established in sheep. The aim of our study was to perform tubal transfer by transvaginal endoscopy in synchronized heifers, in order to expose embryos at various embryonic stages to the physiological mechanisms of migration in the non-ligated oviducts. Various embryonic stages were transferred by transvaginal endoscopy into the oviducts of temporary recipients and were recovered on Day 7. The transfer of embryos in hyaluronate containing medium ("Hyaluronan"), zygotes stripped of cumulus ("Denuded Zygotes"), embryos embedded in cumulus ("Zygotes with Cumulus"), matured oocytes with capacitated spermatozoa ("GIFT") or embryos embedded in Na alginate ("Alginate") led to increasing recovery rates (13, 30, 56, 63 and 71%, respectively). However, the developmental rate on Day 7 was adversely affected (16, 11, 8, 16 and 8%), whereas the blastocyst rate on Day 8 showed more balanced results (17, 14, 18, 21 and 11%). Our data demonstrate that the structural properties of transferred embryos affect tubal migration and are crucial for subsequent in vivo culture. Embryos enclosed in cumulus cells or alginate synchronize more successfully with the oviductal transport systems than denuded stages or embryos in hyaluronate containing medium.