In vitro embryo culture in the production of identical merino lambs by nuclear transplantation

Abstract

This study examined the viability of embryos developed in vitro from 8- to 16-cell stage blastomeres fused with enucleated oocytes. Of 209 blastomeres recovered and subjected to manipulation and electrofusion procedures, 190 (91%) fused successfully, with 86 (45%) of those undergoing cleavage up to the 4- to 16-cell stage when cultured for 66 h in a synthetic oviduct fluid medium. The viability of the embryos was examined by transferring them to recipient ewes and determining the ewes' pregnancy status by ultrasound on Day 45. Of 86 embryos transferred, 14 developed to fetuses in 8 of the 36 recipients, including four sets of identical twins and one set of quads. In contrast, with uncultured and unmanipulated embryos, 15 fetuses developed from 19 embryos transferred at a similar stage of development. The viability of embryos derived from manipulated zygotes cultured in vitro was comparable to that previously reported for studies employing in vivo culture, indicating the potential of in vitro culture systems based on a simple medium for nuclear-transplantation embryos.