Stage-dependent sensitivity of oocytes and embryos to low temperatures

Abstract

Abstract The cryopreservation of mammalian oocytes and embryos has become an integral part of assisted reproduction in animals, especially of domestic species. Embryo cryopreservation of mice and cattle has been remarkable, tens of thousands of live young having been produced by transfer of frozen-thawed embryos. As methods to produce animals in the laboratory by in vitro methods from ovarian oocytes have been improved, embryo cryopreservation has become even more important as a logistical tool; live calves produced from cryopreserved, in vitro-derived embryos are evidence of success. Nevertheless, it is also clear that there is substantial room to improve cryopreservation, in particular as applied to oocytes of most species, porcine embryos, and in vitro-derived bovine embryos. To define the problems more clearly, experiments have been conducted to examine physiological characteristics of oocytes and embryos that render them especially difficult to cryopreserve.