Vitamins and Horses

Horses usually receive an excellent daily dose of the vitamins they require—those they cannot manufacture for themselves—from their forage.

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Vitamins are tiny organic compounds with a huge impact on the health and well-being of your horse. Sometimes gleaned from the diet and sometimes manufactured within the digestive tract, vitamins have the power to promote and regulate virtually all of the body’s normal functions, and they need be present only in minute amounts.

Researchers have classified vitamins into two categories that describe how the vitamins are absorbed, stored, and excreted by the body: fat-soluble and water-soluble. Vitamins A, D, E, and K are fat-soluble vitamins, which tend to be stored in the body (and thus can build up toxicities if there is an excess), while the B vitamins and vitamin C are water-soluble, meaning any excess not used quickly by the body tends to be excreted rather than stored.

Vitamins also can be classified according to their source. Under normal conditions, the horse quite efficiently produces his own vitamins C, D, and niacin (one of the B-complex vitamins) from other organic molecules he ingests. The beneficial microbes living in his cecum and large intestine, as part of their symbiotic bargain, produce all of the other B vitamins as well as vitamin K. Only vitamins A and E are not produced within the horse’s body and must be obtained from vegetable matter in the diet.

In the grand scheme of things, we still don’t know a ton about vitamins. One of the most common misconceptions about vitamins is that “if some is good, more is better.” Horses can become vitamin deficient, and these deficiencies can have devastating effects on their normal functions, but equally dangerous are toxicities from an overdose—a real possibility with some (but not all) of the vitamins.

Furthermore, different species have different vitamin requirements, so assumptions extrapolated from human medicine might not necessarily apply to horses. Vitamin requirements don’t really vary with the amount of work a horse does, either—the pleasure horse and high-performance athlete have almost identical needs. And while we frequently succumb to marketing ploys designed to convince us that our horses are in need of supplemental vitamins in their diet, the reality is that horses usually receive an excellent daily dose of the vitamins they require—those they cannot manufacture for themselves—from their forage.

Vitamin excesses or deficiencies actually extreme enough to cause clinical signs are fairly rare in horses. That’s not to say however, that every diet provides absolutely optimum levels of vitamins. It’s quite possible for a horse to be receiving enough vitamins for maintenance metabolism but not for maximum beneficial health effects.

For example, a real vitamin E deficiency only occurs when a horse takes in less than 10 to 15 international units (IU) per kilogram (kg) of his bodyweight in the dry diet. This is a level easily exceeded by most feeds. But studies have demonstrated that a higher level of vitamin E, along the lines of 50 to 100 IU/kg (more than is delivered by most feeds), might increase a horse’s resistance to infections and to exertion-induced muscle damage. This is a case where some supplementation might produce a beneficial effect over and above what’s required nutritionally. Biotin, which we’ll discuss more in a minute, is another vitamin often fed in excess of the amounts a horse strictly requires to live because it’s reputed to have a beneficial effect on hoof growth and quality. But it’s important to realize that in some cases, such effects might be more old-horseman’s lore than fact. Research is ongoing, and each vitamin must be considered individually before you do any supplementing.

About the Author

Karen Briggs

Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.

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