Cryopreservation of pig embryos: adaptation of vitrification technology for embryo transfer

Great advancements in cryopreservation of pig embryos have been made since the last International Conference on Pig Reproduction (ICPR). In 1997, there were standard methods to cryopreserve germplasm and embryos of most livestock species, except for the pig, and development of this technology for use in the international pig industry was slow and in the early stages. Since 1997, there have been advancements in cryopreservation of pig embryos, with reports of production of live offspring after transfer of frozen-thawed and vitrified-warmed pig embryos. This review summarizes the progress in cryopreservation of pig embryos since 1997. Cellular and molecular biology have been used to understand the hypothermic sensitivity of pig embryos. Development of delipation technology has provided the first evidence that intracellular lipids are linked to hypothermic sensitivity. Cytoskeletal stabilization and vitrification have led to the production of live offspring from vitrified-warmed and transferred embryos. Recently, technology has been developed for cryopreservation of pig morulae. Development of open pulled straws has provided more rapid rates of cooling during vitrification and has been effective for cryopreservation of pig embryos. Although improvements and refinements of the technologies will continue, it is now time for the pig industry to consider cryopreservation of pig embryos as a tool for pig production and for propagation of select herd genetics, while maintaining germplasm resources for the future.