Seminal Plasma Removal Not Needed for All Stallions

Seminal Plasma Removal Not Needed for All Stallions

In the recent past, breeders have routinely removed seminal plasma from stallion semen before cooling—a practice thought to be beneficial to the sperm.

Photo: Anne M. Eberhardt/The Horse

In the recent past, breeders have routinely removed seminal plasma from stallion semen before cooling—a practice thought to be beneficial to the sperm. Now, a group of French researchers has confirmed that, at least for their group of stallions, seminal plasma removal does help stabilize the sperm. However, that stability didn’t appear to make much difference in pregnancy rates.

“For anyone still not convinced, our study goes to show that the functioning of the spermatozoa is very complex—and highly individual,” said Isabelle Barrier-Battut, PhD, researcher at the French National Stud of Le Pin and at the French Horse and Equitation Institute in Normandy. “Biology has never pretended to be an exact science, has it?”

Indeed not. By testing 66 ejaculates from 14 breeding stallions at the country’s National Stud—some of which were considered “poor coolers,” meaning their fertility rates were low with cooled semen—Barrier-Battut and colleagues determined that, in fact, there are no definites when it comes to semen. Different semen's reactions to seminal plasma removal, centrifugation, extenders, cooling, and thawing can be as varied as the stallions themselves.

In her study, Barrier-Battut and her fellow researchers removed seminal plasma from half the semen samples before cooling them in a refrigerator for 48 hours. Once they had been warmed up again to near body temperature, the researchers put the spermatozoa in the samples through a series of tests. First, they evaluated motility by observing speed, direction, straightness, and progression. Second, the team used the hypo-osmostic swelling test, in which they expose the sperm to a special mix of salts and antibiotics. If this makes the flagella (the “tail”) swell, the sperm are considered to be more stable. Finally, the team carried out acrosome (a specialized structure on the head of the sperm that helps penetrate the egg during fertilization) analysis, in which they exposed the sperm to a chemical that’s supposed to mimic some of the events occurring at fertilization and then stained it with a particular dye. The researchers investigated how stained the acrosomes were by using a fluorescent microscope. Their results showed that removing the seminal plasma yielded much better sperm membrane stability, on average. However, individual results varied significantly from one stallion to another.

Motility, on the other hand, was not at all affected by seminal plasma removal. This was true even for the “poor coolers,” Barrier-Battut said, even though previous studies have suggested that seminal plasma removal can improve poor coolers' motility. In fact, in Barrier-Battut’s study, two of the poor cooler stallions actually had worse motility after seminal plasma removal.

Ultimately, when the researchers inseminated mares with semen from the study stallions, sperm membrane stability didn’t seem to have much effect on fertility, Barrier-Battut said. The only factor that made a difference in pregnancy rates was the motility, she said.

She noted that a larger study would be needed to conclusively determine whether sperm membrane quality affects fertility.

“What’s important to know at this stage of the research is that there is great individuality from one stallion to another in terms of his spermatozoa,” Barrier-Battut said. “I wouldn’t recommend centrifuging systematically, or removing seminal plasma systematically, because this can actually be detrimental to some stallions’ sperm. The trick will be getting to know what works for each stallion’s semen, and what’s best for his particular fertility.”

The study, "Removal of seminal plasma enhances membrane stability on fresh and cooled stallion spermatozoa," was published in Reproduction in Domestic Animals

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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