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