Concentration, activity and biochemical characterization of myeloperoxidase in fresh and post-thaw equine semen and their implication on freezability.

The study seeks to understand the role of myeloperoxidase (MPO), a pro-oxidant enzyme, in the movement of thawed horse semen. The research examines the MPO amount, activity, and structure in fresh and thawed semen, and its correlation with the motility of the semen. Results indicate that MPO activity impacts the motility of thawed semen and could potentially predict the quality of thawed semen.

Semen Sample Collection and Assessment

• Semen samples were collected from five stallions, and this process was performed four times.
• The movement of the semen cells was assessed both in their natural state and after thawing.
• The research carried out MPO tests in raw seminal plasma, a dense fraction of sperm collected from semen, and in thawed semen.

MPO Analysis

• The total and active MPO concentrations were assessed using different biochemical tests.
• MPO structures present in semen were also characterized using a method known as Western blot.
• Active MPO was added in saline solution and freezing extender to check its activity during the freezing process.
• Statistical analysis was performed for differences between median values and to establish correlations.

Findings and Conclusions

• Active MPO concentration was found to be low in seminal plasma and thawed semen but high in the semen-rich pellet.
• The inactive MPO precursor was mainly observed in seminal plasma and post-thaw semen; this and other inactive MPO precursor subunits justify the low MPO activity in semen.
• Semen motility after thawing was negatively correlated with MPO activity in the semen-rich pellet. This indicates that higher MPO activity leads to a decrease in semen motility after thawing.
• Significant MPO activity was observed in the semen-rich pellet, and post-thaw loss of activity is partially explained by MPO inactivation in the freezing extender.
• These findings suggest that MPO activity in the semen-pellet has potential as a predictor of how well semen can withstand the freezing process.