Improved methods for freeze preservation of chimpanzee sperm

Freeze preservation of human and nonhuman semen has been used effectively for a number of years; however, the application of freezing to preserve nonhuman primate sperm has been less successful. This study compares five freeze methods and various concentrations of the cryoprotectants glycerol and dimethylsulfoxide (DMSO) for cryopreservation of chimpanzee (Pan troglodytes) sperm. The different methods were compared using quantitative analysis of sperm function and, by an indirect measure of fertilizing capacity, the denuded hamster oocyte penetration assay (SPA). The best results were obtained using an extender comprising Ham's F10 medium containing 15% heat inactivated human cord serum and 15.6% glycerol. Semen extended 1 to 1 by this method, for a final glycerol concentration of 7.8%, and frozen using a computer programmed freezer maintained approximately 65% of its original viability and up to 70% of its initial motility. The extended semen was used to initiate pregnancy in two female chimpanzees.