Association between Myeloperoxidase concentration in equine frozen semen and post thawing parameters

Despite improvement of techniques, semen of 20% of stallions remains unfreezable. Recent studies focused on impact of reactive oxygen species and oxidant enzymes on semen characteristics. Myeloperoxidase (MPO) is a pro-oxidant enzyme contained in and released by neutrophils during degranulation or after cell lysis. It is responsible for the formation of hypochlorous acid, a strong oxidant agent which could damage spermatozoa. The aim of this study was to determine the relation between MPO concentration and characteristics of frozen semen from stallions.
Thirty five straws from different stallions were analyzed. Post-thawing spermatozoal concentration, progressive and total motility were determined by CASA. Freezability was determined according to post-thawing progressive motility (over or under 15%). Percent of alive spermatozoa and abnormal forms were determined after Eosin-Nigrosin and Diff-Quick® staining respectively. Post-thawing MPO concentration was measured by ELISA.
Our study shows that frozen thawed semen contains large amounts of free MPO. We also observed that post-thawing MPO ELISA assay can be used as an indicator of equine semen freezability. High MPO concentration samples showed lower total and progressive motility. A higher proportion of abnormal head shape associated with acrosome reaction was observed in our late examinations of the high concentration MPO group.
Our results show that MPO adversely affects total and progressive motility of equine semen. A negative correlation between normal motile forms and MPO concentration was also observed. The effect of MPO on dead or abnormal forms remains to be precised.