Research has shown that boars can be fed a specific diet to increase fertility, and the same might be true of stallions. Steven Brinsko, DVM, PhD, Dipl. ACT, from Texas A&M University, discussed the potential of feeding a nutraceutical to stallions to enhance their fertility during his presentation at the American Association of Equine Practitioners convention.

He said the nutraceutical, originally developed for boars, was enriched with a specific omega-3 fatty acid to improve semen quality, pregnancy rate, and litter size. Brinsko said research showed that feeding the nutraceutical achieved this by changing the lipid content of semen--in particular by increasing the ratio of docosahexaenoic acid (DHA) to docosapentaenoic acid (DPA). DHA is an omega-3 fatty acid, whereas DPA is an omega-6 fatty acid.

He said it is known that sperm lipids are important for the viability and fertilization potential of sperm. Brinsko said that cooling and freezing semen alters lipids, which contributes to cold shock damage to sperm. It has been found that some susceptibility to cold shock depends on lipid composition within sperm membranes and changing this lipid composition could prevent or reduce the adverse effects of cold shock. One reason the nutritional program was tested for boars is that bull and rooster semen freezes well, but in general, boar and stallion semen does not. Of interest to the Texas A&M researchers was that the lipid content of semen is more similar between boars and stallions than that of bulls and roosters.

Sperm lipids are high in polyunsaturated fatty acids (PUFAs), in particular, DHA and DPA. These fatty acids are obtained primarily from dietary precursors; in other words, the body converts them from PUFAs in what we feed. However, they have competitive enzymatic pathways in their conversion, meaning you can�t just increase DHA precursors alone to increase levels of DHA because linoleic acid (the precursor to DPA) can inhibit the conversion of precursors in feed to DHA. Unfortunately, the fat source of most equine rations is corn and soybean oil, both of which are very high in linoleic acid, the parent compound of DPA. A diet of this nature would favor the conversion to DPA over DHA and could have a negative impact on the quality of stallion semen, including tolerance of sperm to cooling and freezing. It is known that preformed dietary DHA readily transfers to sperm in other species.

Therefore, Brinsko did a study to determine if feeding a DHA-rich nutraceutical would increase the ratio of DHA to DPA in equine semen and whether that would enhance semen quality and improve the response of sperm to cooling and freezing.

Eight fertile stallions were used in the study, with four receiving normal feed and four receiving feed top-dressed with 250 grams of a DHA-rich nutraceutical for 14 weeks. The two groups of stallions were then fed a normal diet for 14 weeks (washout) to allow fatty acid levels to return to pre-treatment levels. Then the treatment groups were reversed and another feeding trial was conducted.
In this way, the stallions acted as their own controls.

Semen was collected at various set times, including pre-treatment, at the end of the first feeding trial, at the end of the washout, and at the end of the second feeding trial. Brinsko said he took 10 ml of raw semen for fatty acid analysis. The rest of the semen was diluted and analyzed as fresh, cooled (stored in an Equitainer for 24 and 48 hours), and frozen samples.

The ratio of DHA to DPA in semen increased when the stallions were fed the nutraceutical. Brinsko said there was no improvement in sperm motility in fresh semen. In semen cooled for 24 hours, there seemed to be an increase in sperm motility in stallions fed the supplement, but this difference was not statistically significant.

In semen cooled 24 hours, Brinsko found a statistically higher percentage of sperm swam straighter and faster when stallions were fed the nutraceutical. In semen cooled 48 hours, Brinsko found an improvement in the percentage of motile sperm, progressively motile sperm, and in percentage of cells swimming rapidly when stallions were fed the nutraceutical.

The most noticeable improvement was seen in semen of stallions considered to be marginal coolers (progressive motility less than 40% at 24 hours), in which average progressive sperm motility improved to 48% at 24 hours and remained at 38% after 48 hours of cooling when they were fed the nutraceutical. Improvements in percentages of motile sperm, and rapidly motile cells were also observed in frozen-thawed semen when stallions were fed the nutraceutical. However, Brinsko said there was quite a bit of variability among stallions.

He concluded that feeding the nutraceutical increased the ratio of DHA to DPA in stallion semen. The quality of fresh semen was unaffected, but the supplement improved the motion characteristics in cooled and frozen-thawed semen.

The ratio of DHA to DPA was increased, but was not optimized by the supplement alone. Brinsko said stallion managers might see more improvement in semen quality by also changing the source of fat in the diet rather than just top-dressing a supplement.

Brinsko said that care needs to be taken when feeding polyunsaturated fatty acids because unless they are processed and stored properly, they can spoil and can lose potency. He said stallion selection is also important. This is something that might be cost-effective for those stallions that have poor to marginal semen quality when it is cooled or frozen, said Brinsko.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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