Ohio State University Extension Bulletin

Horse Nutrition

Bulletin 762-00


Minerals are necessary for most of the chemical reactions occurring in the body and also for the development and maintenance of the skeleton. Macro-minerals include calcium, phosphorus, sodium, and chlorine (salt) and are needed in greatest quantity by the body. Trace minerals are no less important but are needed in smaller amounts.

Calcium and Phosphorus

These two minerals make up 70% of the mineral content of the body, with 99% of the calcium and 80% of the phosphorus in the bones and teeth. Calcium and phosphorus are needed in adequate amounts in the ration but are also needed in the correct ratio. Table 3 lists the needed levels of calcium and phosphorus for various classes of horses. Too much of either one interferes with the use of the other. A ratio of 1.1—2.0 parts of calcium to 1.0 part phosphorus is ideal for the horse. Adult horses can tolerate up to a 5:1 Ca:P ratio without much difficulty. Foals cannot tolerate more than a 3:1 Ca:P ratio.

Neither adults nor foals can tolerate phosphorus levels that exceed calcium levels in the diet. Deficiency or imbalance may result in bone abnormalities, slow growth, contracted tendons, and/or epiphysitis. Table 5 lists several calcium and/or phosphorus sources used to balance these minerals in the feed.


Salt is a combination of the minerals sodium (Na) and chloride (Cl). It is the only mineral compound a horse will actively seek out to eat and should be fed free choice to horses at all times. A mature horse doing light work will consume about 1 oz. of salt daily. However, salt intake is quite variable between horses. As long as a horse has plenty of water available, salt toxicity should never be a problem.

Salt can be provided in block or loose form. The block form is handy to use and decreases waste, but it takes longer for a horse to lick off what it needs. Loose salt is easier to eat, but is often wasted. In general, if a horse needs to consume a lot of salt, such as an endurance horse, loose salt is recommended. Most idle horses and pleasure horses will easily meet their needs with block salt. It is recommended when feeding salt to always use trace mineralized salt. An exception to this may be the horse that is eating large amounts of salt as it might produce a trace mineral toxicity.

Trace Minerals

Ohio is deficient in the trace minerals iodine and selenium, and sometimes deficient in copper and zinc. See Table 6 for a list of the common trace minerals needed by the horse, their required level, and the amount usually present in feedstuffs. Most trace minerals are in adequate supply in the normal ration of the horse. However, feeds grown in Ohio are often lower in these four minerals – iodine, selenium, copper, and zinc – than the table indicates.


The horse needs selenium for normal muscle function and normal function of the immune system. This mineral is a problem because of its narrow range between the requirement and toxic levels. Toxicity is characterized by loss of appetite, loss of mane and tail hair, and in the severe form, blindness, loss of the hoof wall, paralysis, and death.


Iodine deficiency or excess may result in goiter. Some pregnant mares on a seaweed vitamin supplement (high in iodine) have produced foals with goiter, and open mares have had abnormal estrus cycles.


Copper is a marginally deficient mineral in Ohio. It has been identified as aiding in normal cartilage development, the normal change of cartilage to bone, tendon development, strength and elasticity of blood vessels, normal skin pigmentation, fertility, and prevention of anemia. Deficiency is associated with epiphysitis, contracted tendons, lower fertility in mares, rupture of the uterine artery of older mares during parturition, anemia, and depigmentation of the skin around the eyes and muzzle.

The copper level in feeds needs to be evaluated in regard to what other minerals are present in the ration because, in excess, they may combine with the available copper and make it unavailable. Molybdenum, sulfur, and zinc have all been shown to "tie up" copper, making it unavailable to the horse. Possible sources of these three minerals are as follows:

Zinc – galvanized pipes, water and feed buckets.

Sulfur – from water with a high-sulfur content (common in soils with underlying coal).

Molybdenum – common in alfalfa hays (copper deficiency is likely if hay has less than four parts copper to each part molybdenum).

Copper at the level listed in Table 6 is good for a horse, but toxic to some other livestock, especially sheep. Therefore, horse feeds fortified with copper should not be used indiscriminately for other livestock.


Zinc has been recently found to be low (less than 40 ppm) in some rations. It can also be toxic if it exceeds 200 ppm. Deficiency causes reduced growth rates and lesions of the skin on the lower extremities.

All of the trace minerals can be normally supplied by trace mineralized salt. However, if you are dealing with a deficiency in the ration, special high mineral salt may be needed to overcome the deficiency in the normal feedstuffs. There are also some high mineral feeds now on the market to help overcome ration deficiencies.

High mineral broodmare feeds may be especially useful so that the mare may deposit sufficient trace minerals in the developing foal prior to birth and for growth after foaling. Mares milk should provide enough trace minerals for the growing foal for the first two months of life. However, if her diet is deficient then the milk will be also, and the foal will not have its needs met. In this case, you can expect some abnormal growth and development, particularly in the bones.

Because some trace minerals have a narrow range between the needed level and the toxic level, it is best to use commercially prepared preparations instead of trying to add them yourself. Table 6 lists the needed levels in the total ration. Therefore, if the hay portion is very low in a particular trace mineral, the grain portion must be high enough to produce the needed level for the whole ration.

The trace minerals and salt may be added as trace mineralized salt. This can be added to the feed at the rate of 20 pounds per ton of feed and should also be offered free choice. Again, commercial feeds probably already have salt added.

Chelated Minerals

These minerals are often sold to horsemen to improve the digestion of a mineral. The needed mineral is attached to another compound that will protect the mineral from being tied up by other compounds in the diet that may hinder its absorption. Chelates may actually enhance absorption in some cases. Chelated minerals are good if needed, but under most circumstances they are unnecessary and do not justify the added expense.

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