Nutrient Deficiencies in Horse Diets

Nutrient Deficiencies in Horse Diets

If the horse is getting sufficient calories, but is deficient in protein or essential amino acids, his hair coat might get dull, his hoof quality might deteriorate, and his muscle tone might deteriorate.


Horses, like all animals, have a range of nutrient requirements to meet their daily needs. These are spelled out as minimum nutrient requirements in the Nutrient Requirements of Horses, 6th Edition, published by the National Research Council of the National Academy of Science.

If these minimum requirements are not met, the horse may experience deficiency signs. The severity of the deficiency signss may depend on the degree of the deficiency and the time period over which the deficiency exists:

  • A sub-clinical deficiency may be the result of a small deficiency over a period of time. Subclinical deficiencies may also result in decreased immune response, decreased reproductive efficiency and decreased performance.
  • A clinical deficiency is present when there are readily observed or measured symptoms.

Perhaps the easiest example is a deficiency of energy (calories) in the diet. The more severe the deficiency, the faster the horse will lose weight. If a horse is losing a quarter of a pound per day, the loss will take some time to be visible. Over the course of six months, the horse would lose 45 pounds. Over the course of a year, the horse becomes almost 100 pounds underweight or goes from a body condition score 5 to a 3.

If the horse is getting sufficient calories, but is deficient in protein or essential amino acids, the body condition might appear okay, but the hair coat might get dull, hoof quality might deteriorate, and muscle tone might be lost. This is common for horses that are on pasture that has adequate energy content, but is short on amino acids or other nutrients. If the diet is deficient in key fat soluble vitamins—such as A, D and E—it might take longer for the deficiency symptoms to show up as the animal will use up stored vitamins first. Mineral deficiency signs might show as either bone problems or reproductive problems.

Mineral imbalances can create deficiency signs as well. A diet that contains a large excess of zinc might produce symptoms consistent with copper deficiency. An excess of phosphorus, creating an inverted calcium to phosphorus ratio (less than 1:1), can produce nutritional secondary hyperparathyroidism (hyperactivity of one or more parathyroid glands), or “Big Head” disease, as well as other bone issues.

Reprinted with permission from The Feed Room, by Nutrena.

About the Author

Roy A. Johnson, MS

Roy A. Johnson, MS, is an equine technology manager for Cargill Animal Nutrition. In his role, he is responsibile for the development of horse feeds for U.S. business, including feeds for Nutrena, ACCO, Agway, and private label brands. A former professional horse trainer, farm manager, and horse judging coach, Johnson was an assistant professor in the Agricultural Production Division at the University of Minnesota-Wasecae before joining Cargill. Johnson has also participated in a successful Thoroughbred racing partnership.

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