In vivo survival of transferred sheep embryos following puncture of the zona pellucida and in vitro culture

Abstract

This experiment (a 2×2×2 factorial design) investigated the effects on 1- and 2-cell sheep embryos of puncture (ZD) of the zona pellucida, as used in embryo cloning, subsequent in vitro culture for 3 or 5 days 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 development to beyond the 8-cell stage (95%) after 3 days of culture or to blastocysts (74%) after 5 days of culture. However, survival after transfer of embryos cultured for 3 days (41%) was lower ( P<0.01) than that of embryos cultured for 5 days (64%) and this was influenced by an interaction between site of transfer and culture length ( P<0.001). Overall 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 cultured for 5 days, indicating that the zona pellucida may play a protective role during early embryo development. The results demonstrate that the site of transfer of cultured embryos influences their subsequent 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 supports high levels of development and subsequent in vivo survival may be useful for the selection of manipulated embryos for transfer.