Vitamins for Your Horse


Equine Nutrition


What are the nutritional needs of your horse? Misconceptions abound about how much food horses actually require to remain healthy and perform their designated jobs. Understanding Equine Nutrition (Revised Edition) helps horse owners sift through all the ingredients and decide on the best nutritional plan for their horse. The revised edition of Understanding Equine Nutrition contains the latest information from the National Research Council on nutrition requirements for horses.

Author Karen Briggs discusses the different equine food groups in an easy-to-understand manner. Whether the horse is a growing yearling, a high-performance athlete, a weekend pleasure mount, or an in-foal mare, this essential guide will help owners cut through the jargon, sort out the ingredients, and make a feeding plan and menu that is best for their horse. Briggs, a horsewoman and equine nutritionist, resides in Roseneath, Ontario, Canada. She has been a frequent contributor to The Horse: Your Guide to Equine Health Care magazine.

Purchase a copy of Understanding Equine Nutrition (Revised Edition) at

Vitamins: 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 that any excess not used quickly by the body tends to be excreted rather than stored.

Vitamins can also 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.

We still don't know much about vitamins and much of what we do know is misunderstood. 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. Further, 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 (pasture or hay).

Vitamin excesses or deficiencies extreme enough actually to cause symptoms are pretty 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 of his bodyweight in the dry diet. This is a level that is 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 is another vitamin that is 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 still ongoing, and each vitamin must be considered individually before you do any supplementing.

Should you supplement?

Vitamin supplementation might be beneficial in cases like the following:

  • For horses on a high-grain, low-forage diet (such as youngsters in heavy race training), or for those on very poor-quality forage, or eating hay that is more than a year old. Vitamins tend to break down over time in stored feed. For example, there is a 9.5% loss of vitamin A activity in hay every month.
  • For horses receiving prolonged antibiotic treatment for illness or infection. Broad-spectrum antibiotics inhibit the growth of the beneficial cecal and intestinal bacteria, which inhibits their production of B vitamins and vitamin K.
  • For horses in high-stress situations, such as frequent traveling, showing, or racing.
  • For horses who are eating poorly--for example, those recovering from surgery or illness.
  • For horses who are anemic--although the source of the anemia should be determined and treated first.

Vitamins in feed can decompose when exposed to sunlight, heat, air, or the processes that feed goes through in commercial packaging (such as grinding or cooking). Losses during long-term feed storage are greatest for vitamins A, D, K, and thiamin (B1). A is the most crucial of these because the horse does not manufacture this vitamin within his own system. Furthermore, some vitamins are incompatible with each other or with minerals that might also be in the feed. For example, most vitamins are prone to oxidative destruction by iron, copper, sulfates, sulfides, phosphates, and carbonates, all of which might be present in a feed or a vitamin/mineral supplement. The B vitamin thiamin (B1) is incompatible with riboflavin (B2), and both are incompatible with cobalamin (B12) in the presence of light. So feed manufacturers might go to great lengths to protect the vitamins' activity and efficacy, by coating them with gelatin, wax, sugar, or ethylcellulose--harmless, fortunately, to the horse in the amounts required. These compounds might make up a large part of the composition of a powdered or pelleted vitamin/mineral supplement. (Interestingly, it's very difficult to cover vitamins with any sort of protective coating in a liquid format, so many of the liquid supplements rich in B vitamins, iron, and copper, sold as "blood builders," might actually have very little active vitamin content.)

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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