For all the attention they receive, carbohydrates, proteins and fats may seem to be the most important ingredients in your horse’s diet. But vitamins and minerals also play a vital role in a wide variety of his body processes. These organic compounds are readily available from fresh and dried forage and, to a lesser extent, grains. As a result, most pleasure horses can meet their daily vitamin needs by consuming good quality grass or hay.

On the other hand, broodmares, youngsters, elite equine athletes and horses recovering from illness or experiencing stress often require more vitamins than even the best hay can provide. For these horses, a commercial feed formulated for the appropriate stage of life or activity level will typically provide the needed additional vitamins, each in the appropriate amount. Another option is a targeted supplementation—adding a specific vitamin formulation to the daily ration to minimize the risk of inducing a potentially harmful imbalance or excess.

To help you better fulfill your horse’s nutritional needs, we’ve prepared this concise guide to most essential vitamins and minerals in his diet.

1. Vitamin A

Function: chief component of the light-sensitive pigment in the rods of the retina, making it important to vision, particularly at night.  Vitamin A also facilitates cell differentiation and regeneration, playing a critical role in growth and healing.

Source: produced in the body from carotene pigments acquired from green forage and stored in fat cells; excess is kept in the liver for future use.

Imbalance risks: deficiency is rare in mature horses fed adequate forage. Foals deficient at birth may be weak, slow to grow and/or develop night blindness. Excess occurs only through over supplementation; pasture and hay cannot supply the toxic level. Dull coat, fragile bones, poor liver and kidney function may all occur with toxicity.

2. Vitamin B1 (thiamin)

Function: helps metabolize carbohydrates and extract energy from the diet.

Source: produced by gastrointestinal bacteria microflora but in an amount insufficient to meet horses’ needs. Fresh and dried green leaves and cereal grains with husks supply the balance.

Imbalance risks: deficiency is unlikely in horses who receive high-quality forage. However, intestinal disease or parasites can interfere with the vitamin’s synthesis in the gut. Some toxic plants, such as bracken fern, can also inhibit absorption. Signs of deficiency include lethargy, loss of appetite and nervous-ness. Excess is nearly always due to injections given to boost performance horses and signs include excitability, labored breathing and convulsions.

3. Vitamin C (ascorbic acid)

Function: facilitates the synthesis of collagen, the primary component of connective tissue

Source: manufactured in the horse’s liver. Ingested Vitamin C is broken down by gastroin-testinal bacteria before reaching the bloodstream.

Imbalance risks: the body controls production so deficiency is unlikey. Toxicity through supplementation has not been documented.

4. Vitamin D

Function: both forms, D2 and D3, bind to calcium and magnesium to maintain electrolyte balance and bone formation. Also regulates the excretion of phosphates in urine.

Source: synthesized in the body when the sun’s ultraviolet rays combine with a form of cholesterol in the skin; also provided by quality hay

Imbalance risks: deficiency is seen only when induced experimentally. Excess occurs only through over supplementation, with signs including calcification of heart muscle and other soft tissues.

5. Vitamin K

Function: necessary for blood clotting and the utilization of several proteins throughout the body

Source: K1 is found in fresh and dried leafy plants, while K2 is synthesized by gastrointestinal bacteria. A synthetic form, K3, is often included in vitamin supplements.

Imbalance risks: deficiency occurs only when the gut cannot synthesize vitamin K or liver damage makes it impossible for the body to absorb it. Some drugs can also interfere with vitamin K production. Signs of deficiency include internal and external hemorrhaging. Overdose occurs only as a direct a result of injecting K2 when a horse is not deficient. Signs of toxicity include renal damage, laminitis and death

6. Vitamin E

Function: works with the mineral selenium to counteract the potentially harmful effects of oxygen byproducts of normal cellular metabolism known as free radicals.

Source: growing forages, particularly alfalfa, timothy and Kentucky Bluegrass. Grains contain only small amounts of vitamin E.

Imbalance risks: deficiency can occur in horses who do not have access to fresh forage. Signs of deficiency in young horses include rapid degeneration of cardiac and skeletal muscles. In adult horses, certain muscle disorders such as equine motor neuron disease have been linked to relative deficiency. Excess has not been observed

7. Calcium

Function: makes up about 35 percent of your horse’s bone structure and is involved in blood clotting, muscle function and heart-rate regulation. The balance between calcium and phosphorus is critical in bone development.

Source: Alfalfa is a rich forage source of calcium containing 1.24 percent, while timothy hay contains .43 percent and oats only .08 percent.

Imbalance risks: deficiencies result from either low intake or dietary imbalance that leads to inefficient absorption. Calcium-deficit foals can develop rickets, a disease that weakens long bones and enlarges joints. In mature horses, insufficient calcium can cause transient lameness. Excess has been linked to epiphysitis, a disturbance in the conversion of cartilage to bone; this has not been observed, however, when calcium is balanced with other minerals.

8. Iron

Function: oxygen transport and hemoglobin production—iron is critical to a horse’s endurance potential. Although it is common practice to give iron supplements to equine athletes to enhance performance, additional iron provides no benefit unless the horse is deficient.

Source: most forages and grains in ample amounts for horses in all stages of work and development. The horse’s body can absorb more iron from his diet in times of need.

Imbalance risks: With rare exceptions, iron deficiency generally occurs in horses who have had chronic or severe blood loss or long-term parasite damage. When iron stores are depleted from the liver, spleen and bone marrow the horse becomes anemic with marked decrease in exercise tolerance. Iron toxicosis is caused almost exclusively through injected supplementation which bypasses the normal absorption process. Horses with high levels of iron in their blood are more prone to bacterial infection. Foals who receive too much iron may become comatose and die.

9. Phosphorus

Source: hay and cereal grains contain phosphorus, but the form found in hay is much more readily utilized by the horse. Hay grown in phosphorus-depleted soil contains low levels of the mineral; high levels are found in grass in the early stages of growth.

Imbalance risks: A shortage of phosphorus from insufficient intake or dietary imbalance causes bone demineralization and, in extreme cases, spontaneous fractures. The greatest damage in feeding excess phosphorus is from its interaction with calcium. At one time, “big head” disease, in which the bones of a horse’s head enlarge, was a common affliction in those fed a considerable amount of wheat bran, which is very high in phosphorus and low in calcium.

Function: aids in metabolism of carbohydrates, fats and sugars, the utilization of vitamins, and kidney function and cell repair

10. Selenium

Source: Most forages contain selenium, but the amounts vary greatly depending on the area of the country where the forage was grown. For example, the soils of Florida, Northern California and Western Oregon are low in selenium and produce selenium-deficient crops. Meanwhile, soil in parts of Colorado, Montana, Wyoming and Dakotas contain toxic amounts of the mineral.

Function: works in concert with vitamin E to scavenge destructive free radicals and aid in muscle development.

Imbalance risks: A selenium-deficient diet results in reproductive problems, immune deficiencies and, particularly in foals, white muscle disease, where the muscles become weak and useless. Selenium poisoning usually occurs when a horse grazes on plants that contain high levels of the mineral. Horses suffering from acute selenium poisoning may exhibit colic-like discomfort and increased heart and respiratory rates. Long-term grazing on plants that contain high levels of selenium can lead to chronic toxicity and associated anemia, lameness, a rough hair coat and brittle, malformed hooves. Untreated chronic toxicity can be fatal.

11. Sodium chloride (salt)

Function: critical for regulating body fluids and conducting electrical impulses to nerves and muscles.

Source: Unfortified grains and forages contain only very small amounts of sodium, so supplemental salt—in block or loose form—is necessary for all equine diets.

Imbalance risks: Without access to supplemental salt a horse quickly becomes deficient, particularly if sweating heavily or lactating. Slow-onset deficiencies can lead to decreased sweating efficiency, appetite loss, weakness and dehydration. A rapid decline in the body salt supplies results in uncoordinated muscle contraction. Horses tolerate a high level of salt if they have access to fresh water. Signs of salt toxicosis include colic, diarrhea and paralysis of the hind end, and extreme cases can be fatal.

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