Fertilization and Development In Vitro of Bovine Oocytes Following Intracytoplasmic Injection of Heat-Dried Sperm Heads

This study investigated the development of bovine oocytes following intracytoplasmic injection of sperm heads from spermatozoa dried by heating. When sperm suspension was heated in a dry oven at 50, 56, 90, and 120°C, the mean amounts of residual water were about 0.3 g water/g dry weight within 8 h, 6 h, 1.5 h, and 20 min of heating, respectively. Oocyte activation, cleavage of oocytes, and development of cleaved embryos to the morula stage were better in oocytes injected with spermatozoa stored at 25°C for 7-10 days following drying at 50 and 56°C than at 90 and 120°C; however, only a small proportion of oocytes developed to the blastocyst stage. When spermatozoa were dried at 50°C for 16 h, activation, male pronucleus (MPN) formation, cleavage, and development to the morula stage were less good than when spermatozoa were dried for 8 and 10 h and no blastocysts were obtained. The development of oocytes was significantly better when spermatozoa were stored for 7-10 days at 4°C than 25°C after drying at 50°C for 8 h. Longer storage (7 days-12 mo) of heat-dried spermatozoa at 4°C did not affect MPN formation in activated oocytes, but blastocyst development was significantly lower when spermatozoa were stored for 3 mo or more. These results demonstrate that bovine oocytes can be fertilized with heat-dried spermatozoa and that the fertilized oocytes can develop at least to the blastocyst stage.