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<0.01) were observed on cleavage and morula to blastocyst development rates;
percentage of apoptotic, live and dead cells; and expression levels of heat shock protein
70 and interferon tau genes in morula to blastocyst stage embryos. The expression
levels of Bax, Bcl-2 and p53 genes in morula to blastocyst stage embryos were not
different among bulls. The field fertility measured by 60-90 day non-return rate was highly correlated with relative abundance of Bcl-2 mRNA transcripts (r = -0.93) and the
ratio of Bax to Bcl-2 gene expression (r = 0.84). The findings of this study conclude that
variations exist among individual bulls in sperm acrosome reaction, sperm-zona binding
and in-vitro embryo production, apoptosis, and interferon tau and heat shock protein 70
gene expression. Combinations of some of these sperm parameters may be potentially
useful for the accurate prediction of bull fertility in the field.Land and Food Systems, Faculty ofGraduat
