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Effect of Supplementation on Stallion FertilityBy Kentucky Equine Research Staff · February 22, 2012

While research involving horses has been limited, studies in humans, rams, and boars have indicated that fertility and semen characteristics can be improved by supplementation with various nutritional products.

Semen contains a large amount of fatty acids, mainly of the omega-3 and omega-6 types. These components are important in sperm motility, sensitivity to cold shock, and fertilization capacity. In humans, individuals with poor sperm motility had low levels of omega-3 fatty acids as well as a skewed omega-3 to omega-6 ratio compared to those with normal semen quality.

Grain diets for horses are typically higher in omega-6 fatty acids. It was thought that supplementing with omega-3 fatty acids might improve semen quality. A study at Texas A&M University was designed to test this idea. Stallions were fed typical grain diets plus a supplement to boost omega-3 intake. Supplemented stallions showed a three-fold increase in semen levels of omega-3 fatty acids and an improved, though still skewed, semen ratio of omega-3 to omega-6.

Benefits included increases in total motility, progressive motility, and rapid motility of sperm. These changes were most evident in semen that had been cooled and stored for 48 hours. Other results were sperm concentrations that were almost doubled in supplemented stallions and better sperm motility in frozen-thawed semen. Similar studies at other locations resulted in improved total numbers, morphology, and percentages of live sperm in supplemented stallions. In all cases, these improvements were most notable for stallions that had the poorest semen quality initially.

Research in rams showed that sperm motility was greatest for animals having high levels of spermine and spermidine, and low levels of these polyamines have been found in humans with poor sperm motility. These substances are normally produced in the prostate but are also found in radish leaves, radish roots, and oats. In horses, supplementation has not resulted in improved sperm motility, but has sometimes increased libido in slow-breeding stallions.

Supplementation with high levels of vitamins C and E, individually or together, has resulted in increased sperm output, concentration, and motility while decreasing numbers of dead or abnormal sperm in a number of species. Research in Germany and Russia reported improved semen quality when stallions were supplemented with vitamins A, D, and E. In humans, A and C supplementation reduced DNA fragmentation in sperm.

Men with poor sperm motility who were supplemented with L-carnitine and L-acetyl-carnitine had improved motility. Boars supplemented with L-carnitine showed higher semen volumes and sperm concentrations when semen was collected for artificial insemination.

Though it’s tempting to assume that the results of supplementation in one species will be the same in another species, this is not always correct. However, several studies in stallions have shown promising results after supplementation with omega-3 fatty acids. Supplementation may be especially helpful in cases where stallions have marginal fertility or produce semen that does not withstand cooling or freezing. Supplementing stallions that have good fertility and semen that withstands cooling and freezing is probably not going to improve either parameter significantly.