Assessment of sperm quality parameters of six bulls showing different abilities to promote embryo development in vitro.

Experiments were conducted to investigate the possible origins of variation between six bulls showing various blastocyst rates after in vitro fertilisation. No significant difference was observed for the rates of cleavage and 5-8 cell stages, whereas blastocyst yields at Day 6, 7 and 8 post insemination were significantly different between bulls (P < 0.05). Fertilisation rates ranged from 59.5 to 79.3% (P < 0.05), with no difference in the incidence of polyspermy. The proportions of motile and progressive spermatozoa before and after Percoll separation were analysed. A positive effect of Percoll was noted on both parameters (P < 0.05), leading to the absence of difference between bulls after the separation process. Sperm viability and spontaneous acrosome reaction were assessed during 18 h incubation in fertilisation medium. A sharp decrease in sperm viability was observed for all bulls after 2 h incubation, with only 12.6-21.7% of spermatozoa still viable at 18 h. In contrast, the proportion of reacted acrosomes was low in five out of six bulls (<15% at 18 h). In conclusion, the fertilisation rate was the only parameter to show some correlation with blastocyst rate for all bulls.