Name a part of your horse you’d like to enhance–anything from his coat or hooves to his stamina–and there’s likely a supplement for it. Marketed alongside the products that improve joint function and breathing ability, there are supplements advertised to help improve stallion breeding performance. According to Steven Brinsko, DVM, MS, PhD, Dipl. ACT, associate professor of theriogenology at Texas A&M University, early stallion supplements were considered ineffective by veterinarians, "but now it appears there are some products that have the potential to increase fertility," he said.

Brinsko described new developments in stallion nutrition at the Hagyard Bluegrass Equine Symposium 2006, which was held Oct. 18-21 in Lexington, Ky.

It’s All About the Lipids
Central to sperm quality are lipids, which are highly concentrated in the sperm and sperm membranes. "These lipids dictate how the membrane is going to function, and how it reacts to different situations," Brinsko explained. "The cold shock susceptibility (of sperm to cooling or freezing) depends on the sperm’s lipid composition. How these lipids interact with each other is altered with cooling and freezing."

Sperm lipids contain high levels of polyunsaturated fatty acids (PUFA, which are straight-chained fatty acids with multiple double bonds). The semen concentration of PUFAs varies among species: The distribution of PUFAs in stallion sperm is more similar to boars than to that of bulls and roosters. Bulls and roosters produce sperm that are very resistant to cold shock, and they freeze well because of their lipid content. Sperm from stallions and boars have a low tolerance to cold shock and generally freeze poorly