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

Department of Animal Science, the Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan

ABSTRACT

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.

assisted reproductive technology, bovine, fertilization, gamete biology, heat drying, ICSI, oocyte activation, ovum, sperm

¹ Correspondence: FAX: 81 86 251 8388; kniwa{at}cc.okayama-u.ac.jp