Freezing Swine Embryos: Do Success Rates Differ Between Breeds?

University of Nebraska Swine Day Report. Successful freezing, or cryopreservation, of embryos could greatly impact the pork industry, serving as a tool for conservation of valuable germplasm and enhancing biosecurity for transfer of genetic material. Pig embryos are very sensitive to cooling and few reports have shown successful developmental rates following freezing. The objectives of this study were to determine the efficiency of freezing pig embryos using a microdroplet vitrification method and to investigate in vitro development of embryos from Chinese Meishan and occidental white crossbred females following cryopreservation at different stages of embryonic development. Preliminary studies using the microdroplet vitrification method for cryopreservation and embryo transfer into recipient females resulted in the birth of normal, live piglets indicating the effectiveness of this procedure. Rates of expanded blastocyst formation did not differ between Meishan and white crossbred nonfrozen, control embryos (98 and 95%, respectively). Developmental rates were significantly higher for control embryos than vitrified embryosfrom both Meishan and white crossbred females at the expanded blastocyst stage (P < 0.001), but not at the hatched blastocyst stage. Following collection of embryos from Meishan and white crossbred females, cryopreservation and in vitro culture, the percentage of cryopreserved embryos alive after 24 hours of culture was higher for Meishan (72%) than white crossbred (44%; P < 0.001) embryos. However, development of thawed, cryopreserved embryos that survived 24 hours of culture was not different for Meishan and white crossbred embryos at the expanded (64%) or hatched (22%) blastocyst stages. The optimal stages to vitrify pig embryos using the microdroplet method range from late compact morula to early expanded blastocyst. Our results suggest that Meishan embryos have a higher capacityto survive the freezing process than white crossbred embryos, independent of embryo stage.