Published September, 2013

Amino acid. Sounds like something leaking from a Spanish battery, rather than a supplement you’d want to give to your horse.

But an acid isn’t always something that burns or is even “acidic.” In this case it describes a specific order of molecular composition. And amino comes from the word “amine,” which refers to a kind of organic compound.

So yes, they’re fine to give to your horse. No, let’s rephrase that: Amino acids are critical to your horse's health. There are 21 different amino acids used as building blocks to form proteins. Your horse needs all 21 of these building blocks to build those proteins in his body. The power of nature is such that a horse can create 12 of those amino acids himself without a dietary source (other than carbon and nitrogen). For the other nine, however, he’ll need some outside help.

The nine amino acids not created in a horse’s body are called the essential amino acids, which horses acquire through their food. Fortunately, there’s no need to memorize the names of these nine amino acids and make checklists to be sure your horse is getting them through his feed and hay. According to Kristine L. Urschel, PhD, assistant professor of equine science at the University of Kentucky's Department of Animal Sciences, in most circumstances all it takes is feeding your horses good-quality hay and commercial feed adapted to the horse’s age and activity level—and following the specific feeding instructions for that feed.

“Good quality horse feeds have been designed to meet the protein and amino acid requirements of horses as long as they are fed according to the directions,” she said.

Although quality horse feed has been designed with amino acid needs in mind, researchers do sometimes question whether horses are getting the right amount of three of the amino acids in their commercial feeds. Lysine, threonine, and “possibly methionine could be amino acids that we do need to worry a little more about because ‘typical’ ingredients may not provide enough,” said Urschel. “We know more about lysine than the other two (more research has been done), so most commercial feeds include some amount of free lysine (supplemental lysine included in the mix) to make sure requirements are met.”

Amino acids are also provided in grass, Urschel said. But is it enough? “Whether pasture only provides optimal levels of the amino acids for optimal growth or performance or longevity, we still don’t know,” she said, “and this is an area where we need more research.”

Horses do need more amino acids when they’re growing because they’re producing muscles, which are built from proteins, she said. Increasing the feed quantities according to commercial feed directions for young horses should satisfy this increased demand. Whether horses need additional amino acids during periods of intense exercise is not yet clear, but Urschel said she suspects the needs “are likely to change to some extent.” Likewise, as horses reach a very advanced age, they could also need additional amino acids to maintain muscle mass, but research in this area is yet to be carried out.

Some horse owners do like to supplement two amino acids—leucine and tryptophan--because of their supposed effect on horses, Urschel said. Leucine has been shown in some species to promote muscle growth, and tryptophan has been suggested to have a calming effect on horses. However, she says, no research has been carried out on leucine’s effect on muscle growth in horses, and the limited research on tryptophan in horses does not provide much (if any) support for its use as a calming agent.

“For the most part, (supplementing these amino acids) is simply pretty unnecessary,” said Urschel. “There is no benefit to adding amino acids over and above the requirements. It’s a really expensive way to create urine—which is ultimately where the unnecessary amino acids end up.”

Urschel suggested there are better ways of spending your nutrition budget: “From a cost perspective you will be much further ahead to work with an equine nutritionist to make sure the diet meets all of the horse’s requirements than try to micromanage the individual amino acid intakes.”

Christa Lesté-Lasserre is a freelance writer based in France.