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

Abstract

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 degrees 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 micromol/L menadione reduced the proportions of oocytes that cleaved and those that developed to the blastocyst stage; 30 micromol/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 micromol/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.