Components of stallion seminal plasma and their influence on spermatozoa

Abstract

This review focuses on the composition of stallion seminal plasma and on its role as a storage medium of spermatozoa, with special reference to artificial insemination (AI). The stallion ejaculates in 6-9 jets resulting from urethral contractions, and these jets have characteristic volumes, sperm concentrations and composition. Different types of open-ended or closed artificial vaginas (AVs) are available for semen collection, and ejaculatory jets can be collected separately as a fractionated ejaculate, using an open-ended AV or an automated phantom (Equidame ). Seminal plasma influences spermatozoa during storage in different ways depending on dilution ratios, duration of storage and other factors. Beneficial effects have been reported after seminal plasma addition before freezing, but contradictory results show that short-term exposure (15 min) of sperm to seminal plasma has no effect on sperm motility or viability, and prolonged exposure (2, 4 or 6 h) to 5 or 20% seminal plasma in the freezing diluent is deleterious. The optimal proportion of seminal plasma for cooled storage seems to be fairly low. Figures from 0 to 20% have been reported in different studies. There is some evidence that the sperm-rich fractions of the ejaculate would be more suitable for freezing than the whole ejaculate or the sperm-low fractions. Seasonal and individual variation is seen in the composition and quality of stallion seminal plasma. Research on the biochemical composition of whole and fractionated stallion ejaculates, mainly concerning the levels of enzymes, carbohydrates, lipids, electrolytes and minerals, and compounds involved in the protection of sperm from oxidative damage is reviewed.