Q: What roles do specific amino acids play in muscle recovery for performance horses?

A: This is a great question, and I will frame the answer with two general statements: First, a horse’s muscle is made of protein, and amino acids are building blocks for proteins. Second, exertion during physical exercise damages equine muscle tissue and the speed of muscle repair factors into the rate of muscle recovery.

Exertion during exercise causes microscopic tears in the horse’s muscle fibers. These tears and the resulting muscle protein breakdown must happen for muscle strength and mass to increase. When muscle fibers are damaged, satellite cells rush in to fuse the damaged fibers, creating newer, stronger, and larger muscle fibers. Satellite cells are like stem cells for muscles. These precursors to skeletal muscle cells are made of protein and essential for muscle repair. They stimulate the production of more durable muscle which leads to better equine muscle function. However, the building blocks for this repair cycle must be available, which is where dietary amino acids come into play in muscle recovery for performance horses.

Animo Acids and Horse Health

Amino acids and muscle recovery go hand in hand. Twenty standard amino acids make up all proteins in the horse’s body. Equine nutritionists classify amino acids as dietary nonessential, dietary essential (or indispensable), or conditionally essential, based on whether the body can produce them or not. All amino acids are necessary, but the horse can produce nonessential amino acids, either from essential amino acids or from normal protein breakdown. The body cannot produce essential amino acids; these must be supplied by the diet. Horses need conditionally essential amino acids in particular circumstances, such as times of stress, injury, or during illness.

Certain essential amino acids are involved directly in muscle protein turnover, specifically the branched-chain amino acids (BCAAs)—leucine, isoleucine, and valine. However, again, the body needs all 20 amino acids for optimal muscle recovery and function. Supplementing BCAAs alone doesn’t provide the level of muscle recovery support a complete, balanced amino acid supplement provides.

Protein and Amino Acids in Equine Diets

From a dietary standpoint, protein quality describes how well a protein source meets the horse’s essential amino acid requirements. The highest quality protein sources for horses—those that provide higher percentages of essential amino acids—are soybean meal and whey protein. Other protein sources, including flaxseed meal (linseed meal), sunflower meal, distiller’s grains, alfalfa, etc., can provide adequate amounts of total crude protein but will not provide the same essential amino acid balance as soybean meal or whey protein. However, individual amino acids can help improve the essential amino acid balance in the diet.

Dietary protein sources also vary in where the horse digests them in the gastrointestinal tract. The digestion site significantly impacts the ability of that protein source to supply essential amino acids to the body. Proteins digested enzymatically in the small intestine are absorbed as amino acids, whereas proteins digested by microbial fermentation in the hindgut (which includes the cecum and large intestine) are absorbed primarily as ammonia which is excreted in the urine. Even if essential amino acids make it to the horse’s hindgut, no appreciable amino acid absorption occurs in that section of the digestive tract. Therefore, because horses digest forage and other high-fiber ingredients primarily in the hindgut, much of the protein in those feedstuffs can’t provide essential amino acids.

Take-Home Message

A diet containing high-quality protein that can be digested and absorbed in the small intestine helps meet essential amino acid needs and supports muscle recovery and function in performance horses.

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