Equine seminal plasma reduces sperm binding to polymorphonuclear neutrophils (PMNs) and improves the fertility of fresh semen inseminated into inflamed uteri.

This research paper elaborates on how equine seminal plasma (SP) decreases sperm bonding with polymorphonuclear neutrophils (PMNs) and enhances the fertility of fresh semen introduced into inflamed uteri in mares.

Objectives and Methodology

• This study primarily focuses on the immunosuppressive properties of equine SP. It specifically explores its influence on chemotaxis, phagocytosis, and complement activity in vitro.
• The researchers examined the kind and quantity of SP element that stifles sperm-PMN binding in vitro, and the repercussions of this limitation on the fertility rate in mares with uterine inflammation.
• To achieve this, sperm cells were introduced into SP, semen extender, or a blend of both and each mix was then combined with PMN-rich uterine secretions collected 12 hours after artificial insemination (AI).

Findings

• The study reveals that SP significantly reduced the binding between spermatozoa and PMNs.
• After inflaming the uteri, fertile spermatozoa suspended in either SP or semen extender were used to inseminate the mares. The result showed that when spermatozoa were suspended in SP the pregnancy rate was normal (77%). However, when spermatozoa were introduced through a semen extender, the fertility rate plunged to only 5%.
• Moreover, both fresh SP, as well as isolated SP proteins, resulted in a noticeable reduction in sperm-PMN binding.
• Conversely, proteins isolated from either blood plasma (BP) or a skim-milk-based semen extender (SME) did not exhibit a reduction in sperm-PMN binding.

Further Investigation

• The study further sought to understand the difference in concentrations of SP proteins and its effects. They found that the suppression of sperm-PMN binding depended on the doses of SP proteins put to use. For instance, concentrations of 1mg/ml SP protein significantly brought down sperm-PMN binding and 6mg/ml reduced the binding to a level akin to that observed with fresh whole SP.
• Lastly, the researchers discovered that digestion of SP protein with proteinase K led to the complete loss of SP suppressive activity, which confirmed that the factor having an effect is a proteinaceous constituent.