Impact of antifreeze proteins and antifreeze glycoproteins on bovine sperm during freeze-thaw.

There are no reports on the use of antifreeze proteins (AFP) and antifreeze glycoproteins (AFGP) for the use of bull sperm cryopreservation despite studies in the ram, mouse and chimpanzee. The effect of freezing and thawing on bull sperm viability, osmotic resistance and acrosome integrity were observed following the addition of AFP1, AFPIII and AFGP at four concentrations (0.1, 1, 10 and 100 microg/ml). In a second part of the experiment, fluorescein was conjugated to the AFPs and AFGP and observations were made using fluorescence microscopy to determine whether binding occurred between the sperm cell membranes and the proteins. In the final part of the study the cryopreservation media were cooled in the presence of the AFPs and AFGPs at the four concentrations on a cryomicroscope to mimic similar cooling curves as those used in the presence of sperm. Following freeze-thaw, AFPI resulted in increased osmotic resistant cells at 0.1-10 microg/ml compared to the control (P<0.01). AFPI and AFPIII did bind to the sperm cells. There was no visual difference in ice structure between the control, AFPIII and AFGP but AFPI resulted in parallel crystals at 0.1, 1 and 10 microg/ml. We suggest that the increased osmotic resistance in the spermatozoa cryopreserved in AFPI is due to the cells orientating between the ice crystals, reducing mechanical stress to the cell membrane. Previous research has shown that osmotic resistance correlates with bull fertility, suggesting that bull spermatozoa cryopreserved in the presence of AFPI may have increased fertility in vivo.