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Understanding Protein Requirements in Horses: New ResearchBy Kentucky Equine Research Staff · October 24, 2016

Protein plays an integral role in growth, muscle development, and performance. Too little protein stunts growth, affects muscle function, and reduces nutrient transporters and hormones. On the other hand, too much dietary protein negatively impacts the environment, increases ammonia output and adversely affects respiratory health, disrupts acid-base balance, and decreases bone mineralization. Clearly, a fine balance must be achieved, but for horses the fine line between too much and too little remains blurry.

Proteins are made up of chains of amino acids. Many of the individual amino acids have to be consumed from the diet because they cannot be synthesized in the horse’s body. Examples of these “essential” amino acids include arginine, phenylalanine, methionine, threonine, and lysine.

“Lysine is widely believed to be a first limiting amino acid in equine diets, meaning if insufficient lysine is available then growth grinds to a halt,” explained Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research (KER).

One recent study* attempted to clarify the role of lysine in the diets of growing horses. Researchers fed yearlings various levels of lysine, ranging from 76 to 136 mg/kg body weight/day. Blood and muscle biopsy samples were collected, and various amino acids levels, including lysine, were subsequently analyzed using a novel technique to determine the required dietary lysine level in horses.

“This study found that while lysine levels did increase with increased dietary intake, statistical analysis failed to identify a clear dietary requirement for lysine,” shared Crandell.

The researchers therefore suggested that in equine diets “an amino acid other than lysine that is equally limiting across treatment diets could explain why a requirement could not be determined. This limitation would also explain our relatively poor growth rate over the course of the study.”

For optimal horse health, additional research on protein requirements is essential.

Are you supplying your horse—young or old—with an appropriate diet? If you own a young horse, are you feeding a concentrate specifically formulated for growth? Check with a KER nutrition advisor to be sure your horse’s diet is on track.

*Mastellar, S.L., R.J. Coleman, and K.L. Urschel. 2016. Controlled trial of whole body protein synthesis and plasma amino acid concentrations in yearling horses fed graded amounts of lysine. The Veterinary Journal. 93-100.