Cryosurvival of ex situ and in situ feline oocytes

Cryosurvival of feline oocytes preserved as isolated cells (ex situ) or enclosed in ovarian follicles (in situ) has been demonstrated, and significant advances have recently been achieved. However, an ideal protocol for oocyte cryopreservation has not been established to date because of extreme sensitivity of the structural complex to chilling injury. Several factors, such as stage of maturation, membrane permeability and plasticity of the cytoskeleton, affect cryosurvival of the oocyte. Also, intercellular communications between cumulus cells and oocyte are compromised after freezing or vitrification of ex situ or in situ cumulus–oocyte complexes, which has a detrimental effect on oocyte maturational competence. Despite these issues, embryo development, pregnancies and live kittens have been obtained after in vitro fertilization (by ICSI) and transfer of embryos derived from cryopreserved oocytes. It is a general belief that the efficiency of cryopreservation would increase through a better understanding of oocyte responses to cryoprotectants, cooling rates and all the physical events occurring during the exposure of feline oocytes to low temperatures. Cryobanking of feline oocytes would significantly contribute to the preservation of rare genotypes and to the maintenance of a valuable source of genetic material for research applications.