All protein is made up of strings of amino acids. This is why amino acids are often called the building blocks of protein. A horse uses amino acids to create the proteins in muscle, bone, blood, skin, hair, hoof and a variety of other compounds that are critical to healthy growth and maintenance.
There are a total of 22 amino acids. You horse’s body is actually able to make 12 of these, when needed, by breaking down the proteins in its feed and converting their structure. There are, however, 10 amino acids that cannot be synthesized by your horse. They are, in alphabetical order, arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These ten amino acids are referred to as the “essential” amino acids because they must be consumed in feed.
The three essential amino acids required by a horse that are most often deficient in the forage diet are lysine, methionine and threonine. Sometimes you will hear these referred to as “limiting” amino acids. This simply means that if a horse does not receive enough of them in its feed, certain protein synthesis processes will stop once the amino acid is no longer available. The process is “limited” by the absence of the specific essential amino acid.
Look at what each of these three essential amino acids does, and you will understand why a deficiency in your horse’s diet can have such a negative impact on growth and overall health:
- Lysine is responsible for promoting bone growth in foals and maintenance of the skeletal structure in mature horses. It also enhances nitrogen balance and the overall growth of young horses. Lysine deficiency is linked to a variety of developmental orthopedic diseases in young horses, especially in the legs.
- Methionine is critical for the growth and maintenance of coat, hair and hoof tissues. It also promotes the bioavailability of selenium, a critical trace mineral that is also, coincidentally, often deficient in the forage diet. If methionine is deficient in the diet, it will most often be manifest in poor coat, hair and hoof quality.
- Threonine promotes overall growth, muscle mass retention and the efficient use of feed. It also is critical in the production of adrenaline and other important hormones. Threonine deficiency can manifest itself in poor body condition and lack of energy.