Amino Acids 101

Amino Acids 101

There are 21 different amino acids that form proteins in the horse’s body, and horses must acquire nine of those from his diet.

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Have you ever read your horse’s feed or supplement label’s list of ingredients and run across an unfamiliar ingredient? Some of those unfamiliar ingredients might be amino acids, an important part of your horse’s diet. Common amino acids added to equine feeds and supplements include lysine, threonine, methionine, tryptophan, and leucine.

Here’s what you need to know about these important compounds.

What are amino acids?

The term “amino acids” refers to a group of organic compounds that contain nitrogen, carbon, oxygen, and hydrogen. Protein is made up of amino acids strung together. Horses digest proteins and then use the amino acids to help grow and repair bodily tissues. There are 21 different amino acids that form proteins in the horse’s body, and horses must acquire nine of those from his diet. These nine amino acids are known as the indispensable or essential amino acids. The horse can synthesize the remaining amino acids from other dietary components containing carbon and nitrogen.

Why are amino acids important?

A deficiency in just one indispensable amino acid means that the horse is unable to build any proteins containing that amino acid. Such a deficiency halts tissue growth and repair, which are two very important processes for growing and athletic horses. Additionally, amino acids are involved in other metabolic processes, including the formation of neurotransmitters and niacin (an important vitamin).

Photo: Courtesy Sara L. Mastellar, PhD

If amino acids are in proteins, why are they added to feed and supplements separately?

There are several reasons a manufacturer might add amino acids to a feed or supplement in addition to those supplied in protein. First, feed companies could be trying to ensure that their feed is not deficient in a particular amino acid. Little is known about the exact amounts of amino acids horses require or about the amino acid content of the forage a horse consumes, so adding extra to be on the safe side is not an uncommon practice. Additionally, feed ingredients have differing amounts of amino acids in their proteins. For example, corn contains relatively low amounts of lysine, while other ingredients contain substantially more.

Another reason why amino acids might be added is that they are very digestible in their crystalline form. In this form, these amino acids can be absorbed as soon as they reach the small intestine, whereas protein must be broken apart first. Additionally, plant proteins in horse diets are often surrounded by cell walls, which could make the protein less available to the horse if they’re contained in plant material.

Finally, manufacturers might add amino acids individually to capitalize on a particular amino acid’s role in the horse’s metabolism or maintenance of particular proteins. Some amino acids are thought to be particularly important in muscle building, hoof integrity, or neurotransmitter formation. But it’s important to note that much of the reasoning to add specific amino acids to horse diets is based on research completed in other species.

Too much of a good thing?

With all the possible benefits of adding amino acids to equine diets, why not add al of them to all diets? Actually, there are several reasons to avoid oversupplementing amino acids and protein. Horses can only use so much, and that excess must be metabolized and excreted. Horses that are consuming more protein and amino acids than can be used excrete more nitrogen, which can negatively impact the environment. Additionally, that extra metabolism can also decrease heat tolerance, which is problematic for horses competing in hot and humid climates. Finally, protein and amino acids are relatively expensive nutrients to be overfeeding.

Take-Home Message

Amino acids are important to horse health and metabolic function. Feed manufacturers might add amino acids to their feeds and supplements to avoid deficiency, increase digestibility, or for reasons specific to the metabolism of a particular amino acid. But, oversupplementation can result in waste and additional nitrogen excretion, which could be harmful for the environment. If you have questions about whether your horse is consuming enough amino acids in his diet, consult an equine nutritionist or veterinarian before adding supplements to his feeding regimen.

About the Author

Sara L. Mastellar, PhD

Sara L. Mastellar, PhD, is currently an equine instructor at South Dakota State University. She is originally from New York state, where she grew up keeping horses on her parents’ dairy farm and participating in Pony Club and 4-H. She earned a BPS in management specializing in Equine Business Management from Cazenovia College, where she also rode on the Intercollegiate Dressage Association team. She then earned her PhD in equine nutrition at the University of Kentucky. When not teaching or in the saddle, she enjoys spending time with her husband, two dogs, and cat.

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