The Importance of Minerals in Horses' Diets

The Importance of Minerals in Horses' Diets

Of all the ingredients of a horse’s diet, minerals are unique. They make up only the tiniest fraction of the weight of the daily ration, yet they’re critically important for literally dozens of daily bodily functions.

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Of all the ingredients of a horse’s diet, minerals are unique. They make up only the tiniest fraction of the weight of the daily ration, yet they’re critically important for literally dozens of daily bodily functions. They contribute no energy and contain no carbon. In fact, essentially, they’re rocks—and it can be difficult to imagine their being digested by a horse (or by a human, for that matter).

But without minerals, horses could not metabolize fats, proteins, or carbohydrates; their muscles and nerves would not function normally; and their bones could not support their own weight. Minerals help the blood transport oxygen throughout the body, maintain the body’s acid/base and fluid balances, and are necessary components of virtually every enzyme the horse needs for everyday metabolism. They are integral parts of some vitamins, hormones, and amino acids. Yet they make up only about 4% of the horse’s total body weight (as compared to 30% to 35% fats, carbohydrates, and proteins, and about 60% water). In the case of minerals, a little bit means a lot.

Minerals are generally divided into two categories: macrominerals, those needed in larger quantities (relatively speaking) in the daily diet, and microminerals, or trace minerals, those needed only in infinitesimal amounts (usually expressed as parts per million, or ppm—or sometimes as the equivalent unit, mg/kg). Macrominerals, which include calcium, phosphorus, magnesium, sodium, potassium, sulfur, and chlorine (as chloride), are described in g/kg, or as percentages.

In order to provide some perspective, the micromineral “unit,” ppm, is 10,000 times smaller. Iodine, manganese, iron, cobalt, zinc, copper, and selenium are all considered trace minerals necessary to the horse—though the optimum amounts required are, in some cases, still in dispute.

The roles of various minerals in the functioning of the equine body are not always clear cut. Some trace minerals seem to play a role in metabolism, but they have not yet been proven to produce any signs of deficiency when not present: These “mystery minerals” include vanadium, tin, silicon, nickel, chromium, molybdenum, fluorine, and arsenic. It’s interesting to note that some of these are also minerals that can be categorized as “heavy metals.”

But on the other hand, some minerals can do significant damage if ingested in large enough amounts. Potentially toxic are lead, arsenic, nickel, aluminum, and cadmium, all heavy metals that might have a tiny role to play in nutrition.

All minerals can have adverse effects if present in the diet in large enough amounts, but in most cases there is a broad safety zone. Within that safe range, feeding the minimum amount of a mineral might be just as effective as feeding the maximum amount—and often, considerably less expensive. 

Making matters even more complicated is the fact that some minerals have “relationships.” The amount of one mineral present might affect the absorption and utilization of another. Calcium and phosphorus are the most famous partners. Both are essential to the growth and repair of healthy bone, but they must be present in a certain proportion (with at least as much calcium as phosphorus, never the reverse) to do their jobs. Copper, zinc, and iron (with the possible addition of magnesium and manganese) form another linkage that 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.

Finally, the absorption of minerals in the horse’s gut varies widely. Most of these elements can bind in a number of different molecules, some of which are easier for the horse’s digestive system to break down than others. (Zinc, for example, can be found in the diet as zinc carbonate, zinc sulfate, or zinc oxide, to name only three.) The result is that, of the amount of a mineral listed on a product’s feed tag, only a very small percentage might actually be used by the horse. For example, the average absorption of calcium varies between 50% and 75% while phosphorus is less well utilized, at about 30% to 55%. Iron absorption is even poorer; less than 15% is typically used. Zinc’s range is from 5% all the way up to 90%, up to about 25%, but upward of 100% of ingested sodium is absorbed, especially when sweat losses of this mineral are high.

Feed-company chemists have tried to address the absorption problem in a number of innovative ways, some more successful than others. Organic (plant) sources of minerals often are absorbed better than are the inorganic (artificial) sources feed companies might use to supplement a feed—but even this is not a hard-and-fast rule.

For some minerals, absorption can be significantly improved by “chelating” them—a process that bonds minerals to two or more amino acids to form stable biochemical ring compounds, which can be metabolized as much as 300% to 500% more efficiently than their inorganic counterparts. Alas, there is no one magic formula for improving absorption, as what works for one mineral might be a dismal failure with another. This is true even with chelation, which produces very good results with some minerals (including most of the macrominerals) but not all.

Mineral absorption (roughly determined by measuring the amount of the mineral remaining in the manure, compared with the amount contained in the ingested feed) also can be affected by a whole host of other factors. The amount of other nutrients in the diet, such as fats, indigestible fiber, and vitamins, can all have an influence on mineral utilization; so can the pH balance of the gut (which affects the solubility of the minerals).

Nor is the mineral content of feeds etched in stone. It can vary with soil mineral concentrations, plant species, stage of maturity, and conditions at harvesting. All of these factors keep feed industry chemists on their toes as they formulate feeds and supplements for the horse’s maximum benefit. Still, there is much we do understand about the macrominerals and at least some of the trace minerals.

In an article posting tomorrow, we'll take a look at the macro- and microminerals your horse needs in his diet.

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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