Effect of antifreeze proteins on the motility of ram spermatozoa.

The effect of the antifreeze peptide type I (AFP) from Winter flounder, Pseudopleuronectes americanus, and the antifreeze glycoprotein (AFGP) from Antarctic cod, Dissostichus mawsoni, was assessed on the motility of ram spermatozoa (Dorset and Dorset x Romney) after chilling (5 degrees C) and after freeze-thawing. During chilling, spermatozoal motility decreased significantly at an AFP or AFGP concentration of 0.1 microgram/ml and at concentrations above 10 micrograms/ml (P < 0.05). Thus, at 5 degrees C these antifreeze proteins can have a mildly cytotoxic effect at certain concentrations. Addition of AFP or AFGP to the freezing medium at concentrations of 0.1 to 10 micrograms/ml significantly reduced the loss in spermatozoal motility that occurs due to the freeze-thaw process (P < 0.001). The effect was not concentration dependent nor did it depend on which antifreeze protein was added. However, due to the cytotoxicity during the chilling stage, only AFP at a concentration of 10 micrograms/ml increased the percentage of motile spermatozoa significantly following freezing and thawing over that of the control (P < 0.05). Mechanisms to explain the effect of these proteins on spermatozoal motility after chilling and after freeze-thawing are proposed.