Lysine: Making Protein Work
Key Essential Amino Acid Often Deficient In Equine Diets

By Barbara S.Veritas

Why should you know about lysine? Because this essential amino acid is often the key to improving protein availability, especially in grass hay-based diets. Making the proteins that are in the feed available to the horse is one of the most important keys to efficient growth, blood building, tissue repair, and muscle development. By concentrating on improving protein quality and availability, horsemen can avoid the problems and expense of high levels of crude protein. Supplemental lysine is the best approach to achieving this goal.

The protein in the feed cannot be absorbed in its complete form; it must be broken down into smaller units called amino acids and peptides (small complexes of amino acids). After the amino acids and peptides are absorbed, they are recombined in the horse's body to make the thousands of proteins that make a horse. This is why amino acids are often called the "building blocks" of protein. Although there are twenty-two basic amino acids, only eight of them are considered to be essential. By "essential", we mean that the body cannot make them; they must be supplied in the diet. The body can make the fourteen non-essential amino acids if it has adequate supplies of the essential eight. Therefore, if even one of the essential amino acids is deficient in the diet, the production of new proteins is cut short as well.

Lysine is the essential amino acid that is most often deficient in conventional horse diets. Oats, corn, sweet feeds and grass hays are so lysine-poor that the average shortfall for performance horses is estimated at 6 to 10 grams per day. A review of the recommendations of the National Research Council (NRC), as found in Nutrient Requirements of Horses, Fifth Edition, shows how often lysine deficiency can be a problem. Based on several studies, the NRC states that a yearling at moderate growth levels would have a daily lysine requirement of 36 grams. But, based on the average crude protein delivery of lysine (about 3.5%, according to the NRC) in the "typical" diet at the recommended level of digestible energy, the horse would be receiving only 27.7 grams of lysine - a shortfall of 8.3 grams daily.

For two-year olds the picture is no better. The NRC lysine requirement for 2 year-olds in training is 45 grams daily. Based again on the recommended level of digestible energy, the horse would get only 36.8 grams of lysine from the "typical" diet, a shortfall of 8.2 grams daily.

Now, we all know there's no such thing as the "average diet." But the implication is clear that it"s hard to deliver enough lysine, especially for growing horses and those in high-demand activities (e.g., where muscle, blood, or hoof building should be occurring at accelerated rates). It seems a bit backward to be dosing with steroids or gamma oryzinol to build muscle mass when it's likely the horse isn't able to use as much as 50% of the crude protein he's being fed. Lysine is often the first key to making the most of the protein you feed.