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Importance of Dietary Protein in HorsesBy Kentucky Equine Research Staff · December 15, 2011

Protein is important for rebuilding damaged and growing tissues, transporting nutrients in the blood, making blood-clotting factors, and a host of other functions. Growing horses and broodmares usually require more protein in the diet than is provided by forage. Young, growing horses need additional protein to produce muscle and bone, whereas broodmares need it either to nourish the growing fetus or to produce protein-rich milk during lactation. Lucerne (alfalfa), soybean meal, and canola meal are natural sources of quality protein because they contain the necessary amounts of essential amino acids (especially lysine and methionine) and are often included in fortified feeds for horses for that reason. Synthetic sources of lysine and methionine are also available.

If the protein intake of a horse exceeds its requirement, the excess can be used as a source of energy. The amino acids are broken down by the liver, the resulting nitrogen is excreted as ammonia and the carbon units can be used to make glucose or fat. However, it is not recommended to increase the protein concentration of the diet to supply energy because protein metabolism results in an increase in the levels of ammonia in stalls, which can be an irritant to the horse’s respiratory system. Increasing the feed intake to meet the horse’s energy requirements will also increase protein intake, and this should more than adequately meet any additional requirements over and above maintenance levels.