What’s So Special About Lysine?

A nutritionist explains why horses need this amino acid in their diets and what happens if they don’t consume enough.

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Many modern-day commercial feeds add sources of lysine and guarantee those levels in their products. | Photo: Erica Larson/The Horse
Q: What is lysine and why is it included in horse feed?

A: Lysine is one of nine essential amino acids, which are the building blocks that make up protein. I think of them as the letters that make up words where the words are the protein. We give a lot of attention to protein but, in reality, horses do not have a dietary protein requirement; instead, they have a dietary amino acid requirement and, in particular, they have an essential amino acid requirement. This is because essential amino acids cannot be made by the horse the way non-essential amino acids can. Therefore, they must be present in the diet.

The amounts of the various amino acids in the diet and their relative proportions to each other is very important for protein synthesis. Mechanisms within cells take the amino acids that are absorbed from the diet and reconnect them to make the new proteins that are needed by the body. Muscle tissue is the most commonly thought of protein, but there are many other proteins—for example, hormones, enzymes, important components of the immune system, and the keratin that makes hair and hoof tissue.

Each protein has a specific structure and requires amino acids to be available to connect in the right order, like links in a chain. If one of the amino acids needed is present in a smaller quantity than is needed, protein synthesis will be negatively impacted

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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

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