Early embryo development in nuclear transfer clones derived from somatic cells of a high genetic merit dairy cow

Abstract

AbstractThe reported post transfer survival rate to term of cloned embryos derived from both undifferentiated blastomeres and differentiated foetal and adult cells is very low (typically less than 20%). Furthermore, it is acknowledged that there are many technical issues that remain to be resolved to improve the efficiency of nuclear transfer before the technique will find widespread, practical and cost-effective use in multiplying valuable livestock in agriculture. The purpose of this study was to compare early embryo morphology following embryo transfer of nuclear transfer blastocysts derived from somatic cells of an adult Friesian cow with that of standard in vitro-produced embryos. In the present study, 150 embryos were transferred in bulk (i.e., 15, 20 or 25 per recipient) to the ipsilateral uterine horn of 8 recipients using standard non-surgical embryo transfer procedures. Embryos were then recovered following necropsy on either Day 14 or Day 23 of pregnancy and developmental traits described. Embryo recovery and elongation rates were similar on Day 14 of pregnancy (Table 1), although cloned conceptuses were longer and narrower (P<0.05). Embryo recovery and viability rates by Day 23 were similar, although many of the developmental traits appeared more advanced in cloned conceptuses. (Table 1). Allantois development was different because of greater widths and the presence of ‘spurs’ that were not observed with in vitro-produced embryos. We conclude that apparently abnormal conceptus development occurs by about 3 weeks of pregnancy following nuclear transfer, but that embryo survival is not compromised at this early stage of development.