Crude Protein and Amino Acid Levels in Horse Diets

Horses, just like other mammals, require protein, which is made up of amino acids. If any single amino acid is not provided in sufficient quantities, the rate that a horse’s body uses all amino acids to make protein grinds to a slow crawl. But how do you know which amino acid is going to be the snail on the trail?

According to one recent study*, exactly how much of each amino acid a horse needs during each stage of its life is also unknown. Most equine feed labels list crude protein (CP), but information on the amount of individual amino acids is largely lacking.

Minimizing CP while ensuring that each individual amino acid is delivered in sufficient, but not excessive, quantities in the diet will limit dietary wastes, especially nitrogen, which is known to be deleterious to the environment.

To more clearly understand the “flow” of amino acids in weanling horses, the researchers compared the levels of various amino acids in the blood after feeding either:

1. A commercial diet designed for growing horses that provided protein well above recommended levels; or
2. A recommended diet that provided protein levels based on current National Research Council guidelines.

The key finding of the study was that despite following NRC guidelines for CP, weanling Thoroughbreds fed the recommended CP diet had a lower rate of whole-body protein synthesis than in the commercial CP diet. The researchers concluded that there appeared to be one or more “limiting amino acids” that slowed protein synthesis in the recommended CP diet.

More research is clearly needed in this field to reduce nitrogenous wastes through efficient feeding and ensure amino acids are not limited so that horse growth is not negatively impacted.

*Tanner, S.L., A.L. Wagner, R.N. Digianantonio, et al. 2014. Dietary crude protein intake influences rates of whole-body protein synthesis in weanling horses. Vet J In press.