Break down the components of the equine diet and think, for a moment, about what each accomplishes for your horse.
Fiber forms the basis of his energy intake for maintenance metabolism--the everyday, low-key workings of his body. It also stimulates the digestive system and helps keep it functioning.
Protein provides the amino acid "building blocks" for the growth and repair of the body's tissues.
Carbohydrates offer a concentrated energy kick for the faster, harder, longer work you ask of your performance horse.
Fats give your horse a concentrated, easy-to-digest alternative energy source to fuel long-distance work, and they help promote a shiny coat and support the reproductive system. They also assist with weight gain when adding protein is not an option.
The function of minerals and vitamins, however, can't be summed up in a sentence or two. The work they do on behalf of your horse is so varied, so comprehensive, and so amazing that they deserve a little more appreciation than they normally receive. Tiny though these elements may be, they're crucial to your horse's every conceivable function. So let's take a closer look.
Horses might be (approximately) 70% water, but they're also about 4% stone. By that I mean minerals, the inorganic components of the earth that are incorporated into his tissues and play a myriad of roles, from the development and maintenance of his very structure--his bones, muscles, ligaments, tendons, teeth, organs, skin, and hair--to their involvement as enzymatic co-factors in an array of biochemical pathways that keep things running smoothly.
Without minerals, horses could not metabolize fats, proteins, or carbohydrates. Their nerves and muscles could not function normally, and their bones could not support their own weight. Minerals help the blood transport oxygen through the body (iron) and help maintain the body's acid/base and fluid balances. In partnership with various vitamins, hormones, and amino acids, minerals help facilitate all the inner workings of the equine machine.
Horses get most minerals from their feed. But the concentration and availability of the minerals in feed vary with the those in the soil, the plant species, and the conditions under which the plants were harvested, including stage of maturity.
Nutrition researchers have determined the optimum levels of most, but not all, minerals in the equine diet. These optimum levels are important: too little, and metabolic processes might not be able to proceed as they should; too much, and the horse might experience toxicity. Virtually all minerals can have adverse effects if ingested in excessive quantities, but in most cases there is a broad safety zone. (The most notable exceptions to this are selenium and iodine, both of which can be fairly easily overdosed.)
Making matters even more complicated is the fact that some minerals have "relationships" in the equine diet: the amount of one mineral present might affect the absorption and utilization of another. The most familiar "partnership" to most of us is that of calcium and phosphorus, which are both essential to the growth and repair of healthy bone, but they must be present in the equine diet in a certain proportion (with at least as much calcium as phosphorus, never the reverse) in order to do their jobs properly.
Copper, zinc, and iron (with the possible addition of magnesium and manganese) form another, more complex, linkage, which has received a good deal of scrutiny by researchers exploring developmental bone abnormalities in young horses. And there might be many more connections we don't yet fully understand.
The absorption of minerals from the horse's gut into the bloodstream to be distributed throughout the body can also vary widely. Most minerals can bind in a number of different molecules, some of which are easier for the horse's digestive system to break down than others. For example, zinc can be found in the diet as zinc carbonate, zinc sulfate, or zinc oxide, to name only three.
Mineral absorption can also be influenced by the amount of other nutrients in the diet, such as fats, indigestible fiber, and vitamins, and the pH balance of the gut (which can affect the minerals' solubility).
Most nutrition researchers separate minerals into two broad categories: macrominerals, which are needed in relatively large concentrations in the diet; and microminerals, which are needed in very small quantities.
The macrominerals are calcium, phosphorus, sodium, potassium, chloride, magnesium, and sulfur, while the microminerals include copper, iodine, iron, selenium, manganese, zinc, cobalt, and fluorine.
Horses might also have requirements for infinitesimal amounts of other elements, such as chromium, silicon, or even arsenic, but nutrition research hasn't yet determined what exactly these microminerals might do for the horse's metabolism, or exactly how much is needed. It's safe to say, however, that there is probably enough of these substances in the normal equine diet to satisfy the need.
Research into the horse's mineral needs is ongoing, and there were some changes to the recommendations reflected in the latest (2007) edition of the National Research Council's (NRC) publication, Nutrient Requirements of Horses, which is considered by many to be the top reference for equine nutrition.
Brian Nielsen, MS, PhD, PAS, Dipl. ACAN an assistant professor of equine nutrition at Michigan State University, was one of the committee members involved in assembling the revised NRC recommendations. If he could offer one take-home message to horse owners about mineral supplementation, it would be: "Don't oversupplement. I see a lot of problems caused by well-meaning people who are trying to tinker too much with the diet. It's important to remember that minerals tend to interreact and compete with each other for absorption.
"If you're feeding good forage, and a commercial concentrate with a mix of grains which has been formulated to provide a balanced diet, then that should be all you need in 99% of cases," he says. "When you tinker with the levels by adding a little of this and a pinch of that, you upset the balance and can potentially do more harm than good."
Shannon Pratt-Phillips, MSc, PhD, an assistant professor who teaches equine nutrition and exercise physiology at North Carolina State University, agrees. "Personally, I still feel people don't appreciate what's already in their forage," she says. "There is far too much dependence on grain and on supplements to supply the minerals needed in the equine diet, when a hay analysis will often reveal that the forage is already doing a good job of meeting the horse's nutrient requirements.
"When you supplement on top of good forage and a commercially fortified grain ration--especially when you oversupplement one nutrient in particular--you risk interfering with the absorption of other nutrients," she adds.
Vitamins don't register very significantly on the scales when you compare them with nutrients like fiber, carbs, or protein, but as with minerals, their impact on the health and well-being of your horse far exceeds their molecular weight.
Sometimes sourced from the diet, sometimes manufactured by the horse himself, vitamins have the power to regulate most of the body's daily functions, even though they're present in minute quantities.
Vitamins are sorted into two categories, fat-soluble and water-soluble, which describe how the vitamins are absorbed, stored, and excreted by the body.
Vitamins A, D, E, and K are the fat-soluble vitamins, which tend to be stored in the body's fat stores (and, thus, can build up, causing toxicities if there is an excess), while the B vitamins and vitamin C fall into the water-soluble category, meaning that any excess not used by the body tends to be excreted rather than stored.
Under normal grazing conditions, the horse produces his own vitamins C, D, and niacin (one of the B-complex vitamins) from other organic molecules he ingests. (Horses in stalls can be low in D, as it requires sun exposure.) The beneficial bacteria living in his digestive tract, as part of their symbiotic bargain with his body, produce all of the other B vitamins he needs, as well as vitamin K. Only vitamins A and E are not produced within the horse's body and must be obtained from the diet.
Vitamin requirements don't really vary with the amount of work a horse does. Pleasure horses and high-performance athletes have almost identical needs.
Just as with minerals, it is possible for horses to become vitamin-deficient, and these deficiencies can have devastating effects on their metabolism and function. But equally dangerous are toxicities from overdoses. However, extreme vitamin excesses or deficiencies that cause clinical signs are rare in horses, except when there is malnutrition present or when a horse has been severely oversupplemented.
"The average horse on the average diet is getting his vitamin needs met," Nielsen maintains. "The microbes in the horse's gut do a good job of synthesizing most vitamins on their own, so vitamin deficiency is not typically a problem.
"There were not a lot of huge, sweeping changes in the vitamin section of the new edition of NRC," he adds. "But that's due, in part, to the fact that not much new research has been done."
Pratt-Phillips says consumers can become confused about vitamin supplementation, particularly because some vitamins are thought to have therapeutic effects when fed over and above the requirement for basic good health. Biotin is one example. Most horse people know this B vitamin has a reputation for improving the quality of hoof growth when fed in (relatively) high dosages. Recent interest in the beneficial effects of antioxidants (substances which harvest free radicals, the unbound electrons that can accelerate cell damage in the body) has put vitamin E in the spotlight as well for its purported antioxidant effects. But is it really to your horse's benefit to hypersupplement vitamins like this?
Nielsen says, "The jury's still out. On the antioxidant side, most studies so far haven't demonstrated drastic differences in performance (when comparing horses given vitamin E as an antioxidant and those in control groups).
"Even with biotin research, it's hard to say whether it really makes a difference because it's hard to control all the seasonal variables affecting hoof hardness," he adds. "If you feed a biotin supplement and your horse's hooves improve, can you really say the supplement made the difference when so many other environmental factors are changing every day?"
Both Nielsen and Pratt-Phillips stress that it's pivotal for horse owners to discern the difference between anecdotal evidence and testimonials versus scientifically valid research before they put their money down on a supplement.
Delivering a good balance of vitamins and minerals in your horse's diet is important, but the optimal way of doing that is to provide him with good-quality forage and a commercially balanced, professionally formulated mix of grains.
About the Author
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.
POLL: University Equine Hospitals