Consequences for the bovine embryo of being derived from a spermatozoon subjected to oxidative stress

Objective To determine whether oxidative damage of ejaculated frozen–thawed sperm prior to oocyte insemination in vitro affects the competence of the resultant embryo to develop to the blastocyst stage. Method Extended frozen semen from bulls was thawed, subjected to Percoll gradient purification to obtain motile spermatozoa and mixed with medium containing the pro-oxidants menadione or tert-butyl hydroperoxide. After 3 h at 38.5°C, the sperm were washed and used to inseminate oocytes in vitro. Embryo development proceeded until 8 days after insemination. Results Treatment of sperm with 15 or 30 µmol/L menadione reduced the proportions of oocytes that cleaved and those that developed to the blastocyst stage; 30 µmol/L menadione reduced the proportion of cleaved embryos that developed to the blastocyst stage at day 8 after insemination. Oocytes inseminated with sperm treated with 150 or 300 µmol/L tert-butyl hydroperoxide had lower proportions of cleavage and blastocyst development, and the proportion of cleaved embryos becoming blastocysts was also reduced. Conclusion Oxidative damage to ejaculated sperm can compromise the ability of the sperm to cause oocyte cleavage and leads to formation of embryos with reduced competence for development.