Avian semen cryopreservation: what are the biological challenges?

The value of the ability to cryopreserve and store germplasm has long been recognized for indefinite preservation of genetic material, especially for at-risk populations. In contrast to domestic livestock species, cryogenic storage of poultry semen is not reliable enough for germplasm preservation. The relatively low fertilizing ability of frozen/thawed poultry sperm most likely results from physiological sensitivity to the cryogenic process coupled with the requirement for prolonged sperm functionality in the hen reproductive tract; however, the concept of defining these physiological challenges has been underemphasized. For example, alterations in membrane carbohydrate content and diminished energy production in frozen/thawed sperm have important implications for successful gamete interaction. Recent data suggests that both glycoconjugate content and adenosine triphosphate (ATP) generation are affected by cryopreservation. Moreover, susceptibility to the cryogenic process seems to vary among lines and strains of birds, as illustrated by line-specific differences in ATP concentrations of frozen/thawed sperm from pedigreed commercial layers. Research based on biochemical and molecular comparisons of sperm among lines may lead to identification of factors that influence the freezability of poultry semen.