Published February, 2015

Kristine Urschel, PhD, associate professor of equine science in University of Kentucky’s (UK) animal and food sciences department, gave a talk about horses' amino acid requirements at the 4th Annual UK Equine Showcase, held Jan. 23 in Lexington, Kentucky.

Amino acids are one of the most significant pieces of the puzzle in a horse’s diet, she explained. They benefit all of a horse’s vital processes, as they are used to build all the protein in the body.

Horses require a total of 20 amino acids to build their body’s proteins. The horse's own body can make 11 of those amino acid but does not have the ability to create the remaining nine it needs. Some amino acids can only be made by plants and micro-organisms. These are called the essential amino acids, and a horse must obtain them from food.

“Most mature horses will meet all requirements for their amino acids by being fed a good-quality forage and concentrate and by following the specific feeding instructions for that particular feed,” Urschel said.

Amino acids that most commonly fall below the equine body's required amount are called limiting amino acids. The amino acids most likely to be limiting in a horse’s diet are lysine and threonine, which determine how well a horse can use all other amino acids. Amino acids cannot be substituted for each other, and if all amino acids are not present, protein synthesis is limited.

In a recent study, Urschel found that limiting amino acid problems occurred more frequently in younger, growing horses than in mature horses.

If you’re worried about whether your horse is receiving enough limiting amino acids, Urschel said you should, “ read the labels on most horse feeds; you’ll see that they already have some amount of free lysine included into the mix to meet requirements.”

The study of amino acids in horses is ongoing. In future studies Urschel would like to look at limiting amino acids in lactating mares, during gestation, and during intense exercise.

Alexandra Harper, MBA, is the operations and communications coordinator for the UK Ag Equine Programs.