DEVELOPMENTAL POTENTIAL OF IN-VITRO PRODUCED BOVINE EMBRYOS FOLLOWINGCRYOPRESERVATION AND SINGLE-EMBRYO TRANSFER

Information on the developmental potential of in vitro-produced, cryop reserved bovine embryos following single-embryo transfer to synchroniz ed recipients is limited. The aim of this study was to compare the pre gnancy rates of vitrified, conventionally cryopreserved, and control ( unfrozen) in vitro embryos. The embryos were cryopreserved either by V itrification in Solution 3a (VS3a) or by conventional slow freezing in 10% glycerol. Forty-two percent (n=121) of the recipients established pregnancy when in vitro produced morulae to expanded blastocyst stage embryos were transferred immediately following culture. Significantly more morulae on Day 7 and 8 of culture established pregnancy (11/14) than blastocysts on Days 7 to 9 of culture (40/107; P<0.05). Significa ntly fewer biastocysts on Day 9 of culture established pregnancy (12/3 5) than those on Days 7 and 8 of culture (39/86; P<0.05). Cryopreserve d embryos yielded significantly fewer pregnancy rates than freshly tra nsferred embryos (P<0.05). Twenty-three percent (n=85) of vitrified em bryos and 14% (n=35) of conventially frozen embryos established pregna ncies. When cryopreservation methods were compared in terms of embryo stage, vitrification did not yield significantly better results than t he conventional freezing method, but this might be due to the low numb er of conventionally frozen embryos transferred. These data indicate t hat in vitro produced embryos yield high pregnancy rates when transfer red immediately following in vitro culture for 7 or 8 d to the morula and blastocyst stages. Cryopreservation of in vitro produced embryos e ither by vitrification or conventional freezing reduced their ability to establish pregnancy. Vitrification was found to be the more practic able method; therefore, when transfer of fresh embryos is not possible , vitrification should be preferred to conventional freezing methods.