Characterization of Phosphatidylserine Expression in Bovine Sperm

Many factors influence male fertility, and conventional fertility evaluations are not able to reliably identify sub-fertile animals. The overall goal of this work was to explore the expression of phosphatidylserine (PS) on bovine sperm and investigate what factors may impact it, as previous research demonstrated that phosphatidylserine (PS) plays a role in murine fertilization. Despite conventionally being an apoptotic marker, it is present on viable and fertilization-competent murine sperm, however, less is known of the possible role of PS in bovine fertilization. In experiment 1, viable bovine sperm cells expressing PS were identified and PS levels in fresh and frozen semen were compared. Phosphatidylserine levels in frozen samples were significantly less than in fresh samples. We conclude that the cryopreservation process has an impact on PS expression in sperm by altering the proportion of sperm cells which are capable of fertilization. Experiment 2 examined PS levels in bulls with varying fertility levels based on sire conception rate (SCR). There was no difference in PS levels between high and low fertility bulls. There was a significant difference in PS levels of uncapacitated samples and those capacitated for one hour. These results warrant further investigation into the role of phosphatidylserine in bovine fertilization.