Cryopreservation of embryos in farm animals

Abstract

Cryopreservation of mammalian embryos was developed during the late 1970s. Since then, the cryopreservation techniques have been diversified and improved to try to cryopreserve embryos from most species, at different developmental stages, and more sensitive embryos such as in vitro produced, cloned or biopsied embryos. Slow freezing (or equilibrium freezing) and vitrification are the main cryopreservation techniques commonly used. Slow freezing attempts to maintain a delicate balance between cryoprotectants and the aqueous embryo compartment, whereas the strategy of the vitrification method is a rapid solidification of liquid without ice crystal formation. The OPS technique (Open Pulled Straw) is a faster vitrification process. All techniques offer advantages and disadvantages, but slow freezing is currently the most used on farm applications in sheep, goats and cattle with embryos produced in vivo. In pigs, only the OPS technique allows to cryopreserve embryos with good success. In the equine, none of these different techniques gives good results : only a few foals have been born after transfer of cryopreserved embryos.