Birth of cloned pigs from zona-free nuclear transfer blastocysts developed in vitro before transfer

The objective of this work was to obtain cloned pig offspring by uterine transfer of blastocysts produced by zona-free manipulation. We started by defining the most suitable culture media for growing pig nuclear transfer embryos produced by zona-free micromanipulation comparing NCSU-23aa with Synthetic Oviduct Fluid (SOFaa) and with in vivo culture in the sheep oviduct. We found that parthenogenetic development to day 7 blastocyst in NCSU-23aa and sheep oviduct was significantly superior as compared to SOFaa (61.8%, 64% and 42.4 respectively) although blastocyst cell number was higher in the latter. Interestingly, when we compared the two media for the culture of nuclear transfer (NT) embryos derived from 3 different donor cell lines, we observed lower rates of development with NCSU-23aa (from 24.5% to 32.4%) while with SOFaa the development was significantly higher for two donor cell lines as compared to the third (44.4%, 48.9% and 20.6% respectively). A total of 244 blastocysts grown in SOFaa were transferred in four synchronized sows on day 5 or 6 of development. Two recipients farrowed 6 and 8 piglets corresponding to an efficiency of development to term of 8% and 16% of the transferred embryos respectively. Eleven pigs are now 10 month of age and those that have reached puberty have been proven to be fertile. Finally, this is the first report on the production of cloned pigs derived from the transfer of NT embryos at the blastocyst stage.