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
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.