Like a structure made of tinker toys, protein is composed of smaller pieces–the amino acids. These can be rearranged to form the different types of protein-based tissues in the body. Protein is one of the basic nutrient elements of the equine diet, along with fats, carbohydrates, vitamins, and minerals, and it is necessary to the life and well-being of the horse. Crucial for tissue growth and repair, protein builds bones, blood, skin, hair, and muscle.

What is Protein?

Sarah Ralston, VMD, PhD, Dipl. ACVN, associate professor in the Department of Animal Science at Cook College, Rutgers University, says, “Proteins are chains of amino acids in various combinations. There are 22 from which to choose. They have a linear structure (the sequence of amino acids) and secondary and tertiary structure, where amino acids fold back on themselves and have linkages, looking like they are tied in knots. The structure gives a protein its properties.”

Muscle proteins are different from enzyme or hormone proteins, and they differ greatly from the wide variety of proteins in blood, for instance.

“Proteins are continually being turned over in the body,” says Ralston. “There is a constant sequence of breaking down and resynthesizing, according to need.”

The horse can synthesize most of the amino acids he needs, but some essential ones, like lysine, must be obtained from feed. If even one essential amino acid for a protein is missing from the diet, synthesis of that particular protein cannot continue. If the missing amino acid is necessary to a certain phase of body growth, its absence will prevent normal growth even if the diet contains enough of all the other ingredients. Young horses on diets low in lysine grow more slowly than those fed adequate lysine, according to the National Research Council’s Nutrient Requirements of Horses.

Ray Geor, BVSc, PhD, Dipl. ACVIM, i