The ability to cryopreserve germplasm banks of frozen embryos indefinitely allows genetic diversity to be preserved. Cattle embryos can be successfully frozen and stored indefinitely at -196°C in liquid nitrogen. Cryopreservation is a multistage process incorporating a cryoprotectant or antifreeze, and the thawing and transfer of embryos are carried out in a manner similar to frozen-thawed semen. Following freezing and thawing, pregnancy rates of up to 45 to 50% are currently achievable.
In contrast to embryos, oocytes (eggs) are extremely sensitive to chilling and are difficult to cryopreserve. The development of new cooling technologies using liquid nitrogen (LN2) cooled below -196°C (LN2 slush), however, has enabled the efficient cryopreservation of oocytes. There is research in cryopreservation of ovarian tissue that researchers say will become a reality, enabling the preservation of pure genetic stocks of female as well as male gametes.
