Many horse owners feel intimated when discussing or reading about some of the finer details of equine nutrition, but they shouldn’t. The basics of equine nutrition are relatively simple to understand, and I think every horse owner owes it to themselves and their animals to know as much as they can about the nutritional needs of their equine companions. This is probably no truer than when discussing amino acids in the equine diet.
Now, don’t be intimidated. I am almost certain you have heard the term “amino acids” before and you may be very knowledgeable on the subject. In any case, it is worth a review of what amino acids are and why they are critical to the appropriate physical development and maintenance of your horse.
So what are amino acids? Well, 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 wide variety of other tissues that are critical to healthy growth and maintenance. All animals, including horses, get the amino acids their bodies require in one of two ways: they either consume them in feed, or they synthesize them in their bodies by breaking down protein and converting one type of amino acid into another. If an animal is unable to synthesize a specific amino acid, this is called an “essential amino acid” for that specific animal. This simply means that the only way that animal can get that specific amino acid is by consuming it in its feed.
There are a total of 22 amino acids. Your 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. These are the “essential” amino acids for horses. They are, in alphabetical order, arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.
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 for a horse, 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.
Now, just because you are feeding your horse a diet that is high in protein does not mean it is receiving enough of the essential amino acids. Alfalfa, for example, is high in protein but is commonly deficient in the three essential amino acids outlined above. Some people call this “poor-quality” protein. Grass and grass hays, on the other hand, usually have “high-quality” protein. In other words, of the protein they do contain, it has a lot of the essential amino acids. The problem with these types of forages, however, can be that they simply do not have enough of this high-quality protein.
So although you may be feeding your horse plenty of protein, as in an alfalfa diet, or high-quality protein, as in a grass hay diet, if the essential amino acids are not present in sufficient quantities, your horse will still be deficient nutritionally and may suffer from things like a poor hair coat, weak topline or poor hooves. To solve these problems, the easy solution is usually to add a simple, good-quality ration balancer (such as Dr. Thornley’s Hay Balancer®) that specifically contains adequate amounts of lysine, methionine and threonine to your horse’s daily forage ration. It is a simple thing that can make a significant difference in your horse’s health.
This information is not meant to diagnose or prescribe treatment for any equine health problem. If you suspect your horse is suffering from any health problem, consult your veterinary professional for complete testing, diagnosis and treatment.
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