They purport to “Increase power.” “Delay fatigue.” “Increase stamina.” “Build muscle.” “Reduce recovery time.” “Extensive research has proven…” Doubtless, most of you have seen and read advertisements for nutritional supplements in which the manufacturers make these and other similar claims. In the past decade or so, there has been a tremendous increase in the array of nutritional supplements marketed for use in horses, as evidenced by the huge number of small buckets, tubs, and tubes that line the shelves of tack shops and feed stores. These supplements might contain a specific nutrient or ingredient, or a mixture of ingredients. Of course, the current marketing buzzword for some of these supplements is “nutraceutical,” defined as a nutrient that, when taken in large doses, will improve some aspect of body structure or function (see the supplements article in The Horse of February 2000).

In this article, we will consider some of the nutritional supplements that are purported to boost performance in horses. In essence, the major implication of the persuasive advertising referred to above is that administration of these supplements will improve a horse’s exercise performance capacity. That is, the horse will be able to run faster, run longer before fatigue, and/or recover more quickly following exercise.

Just how valid are these claims? Can we realistically expect a nutritional supplement to boost a horse’s performance? Are there any risks associated with use of such supplements? Unfortunately, for many of the supplements on the market, it is difficult to judge their effectiveness because there is little or no scientific information available. In many instances, there is no understanding of the function a given supplement might have in the body. Even worse, we cannot be sure that the supplement, when ingested, i