Individual bull variations on sperm acrosome reaction, sperm-zona binding, in-vitro embryo production, and preimplantation embryo apoptosis and gene expression

The overall objective of this study was to develop in-vitro tests to predict fertility of bulls in the field. The specific objectives were to investigate 1) the bull effect on sperm acrosome reaction, sperm-zona binding and in vitro embryo production (experiment 1), 2) the effect of sperm pre-incubation time and sperm concentration of bulls on in-vitro fertilization (experiment 2), 3) the bull effect on apoptosis and expression of Bcl-2, Bax, p53, interferon tau and heat shock protein-70 genes in bovine preimplantation embryos produced in-vitro (experiment 3), and 4) the correlation between the above in-vitro tests and the field fertility data. In the first experiment, prefreeze motility, acrosome reaction at 0 h, increase in acrosome reaction at 4 h and sperm-zona binding were different (p<0.05) among bulls. Significant correlations were observed between individual sperm parameters. None of the in-vitro tests was correlated with non-return rates (field fertility data). In the second experiment, significant bull effects were observed on fertilization, when using short and long sperm pre-incubation time with normal and high sperm:oocyte ratio. When using normal sperm:oocyte ratio (25,000:1), the percent difference in normally fertilized zygotes between short and long sperm pre-incubation times showed high degree of correlation with non-return rates (r = 0.90; p<0.05) of the experimental bulls. In the third experiment, significant bull effects (P