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Choose Quality Protein for Horse DietsBy Kentucky Equine Research Staff · June 13, 2012

Eighty percent of the horse’s fat-free, moisture-free body composition is protein. Protein is a predominant component of blood, muscles, organs, and enzymes and it is a critical part of the horse’s diet. The age and use of the horse are the most important considerations in determining protein requirements. In addition, there are several other important factors concerning protein which should be evaluated when selecting a ration for a particular phase of a horse’s life. One of these is protein quality.

Many of the amino acids that make up the body protein of horses must be supplied in their diets. These amino acids are classified as being essential for growth and reproduction. Sources of feed protein that contain an assortment of amino acids that approximate the needs of the animal are considered high quality (high biological value), while those that do not are considered low quality. The amino acid most likely to be deficient in the diets of growing horses is lysine. Various researchers have done a great deal of work to determine the requirement for lysine in growing horses. This research has shown that horses fed diets deficient in lysine will grow more slowly than horses fed a diet high in lysine, even if the crude protein percentages of the diets are identical.

Studies at the University of Florida suggested that the second limiting amino acid for growing horses may be threonine. Yearlings fed corn/oats/soybean meal diets along with coastal bermudagrass hay grew faster with additional muscle gain when threonine was added to the concentrate at a level of 0.1% of the grain mix.

Several different sources of supplemental protein are commonly used in horse feeds. These include milk proteins, alfalfa meal, and a number of byproduct meals made from the production of oils such as soybean meal, linseed meal, cottonseed meal, safflower meal, and sunflower meal. What is often overlooked, however, is the amount of protein and lysine supplied by the grain portion of a horse ration. Typically, the grain portion (corn, barley, oats, etc.) contributes about 40 to 50% of the total protein of a feed for growing horses. The amount of lysine supplied from these cereal grains, however, is only about 30 to 40% of the total, since cereal grains are fairly low in lysine. Therefore, the supplemental source of protein used in horse feeds should be high quality. Alfalfa, milk proteins, and soybean meal are all good sources of quality protein for growing horses. Protein supplements which are deficient in lysine include linseed meal, cottonseed meal, and peanut meal.