IN-VIVO SURVIVAL OF TRANSFERRED SHEEP EMBRYOS FOLLOWING PUNCTURE OF THE ZONA-PELLUCIDA AND IN-VITRO CULTURE

This experiment (a 2 x 2 x 2 factorial design) investigated the effect s on 1- and 2-cell keep embryos of puncture (ZD) of the zona pellucida , as used in embryo cloning, subsequent in vitro culture for 3 or 5 da ys in synthetic oviduct fluid (SOF) plus 20% human serum, and transfer of these embryos to the uterus or oviduct of synchronised recipients (three embryos/recipient) on their subsequent development to recipient slaughter at Days 14 or 19. There was no effect of ZD on in vitro dev elopment to beyond the 8-cell stage (95%) after 3 days of culture or t o blastocysts (74%) after 5 days of culture. However, survival after t ransfer of embryos cultured for 3 days (41%) was lower (P<0.01) than t hat of embryos cultured for 5 days (64%) and this was influenced by an interaction between site of transfer and culture length (P<0.001). Ov erall the survival after transfer of ZD embryos was lower than that of intact embryos (42% vs. 55%, P<0.05) and an interaction was observed between ZD and culture length (P<0.05). ZD embryos cultured for 3 days were less viable than intact embryos cultured for 3 days or embryos c ultured for 5 days, indicating that the zona pellucida may play a prot ective role during early embryo development. The results demonstrate t hat the site of transfer of cultured embryos influences their subseque nt survival; embryos cultured for 3 days should be transferred to the oviduct and 5-day cultured embryos should be transferred to the uterus . Culture of embryos to post-compaction stages in a system which suppo rts high levels of development and subsequent in vivo survival may be useful for the selection of manipulated embryos for transfer.