Protein Demystified

It’s all about amino acids

Protein is a major component in most tissues in the horse. Proteins are made up of individual amino acids that join together to form chains. The length of the protein chains varies from protein to protein, as does the combination of amino acids making up the chains.

When horses consume proteins in their diet, the proteins are broken down and absorbed as amino acids. These amino acids are then circulated in the blood and reconstructed into new proteins as needed.

In horses, protein is digested and adsorbed in the foregut (stomach and small intestine). The proteins that escape absorption in the foregut are utilized by the microbes (bugs) in the hindgut. Although the bugs benefit from this protein, it does not add to the horse’s circulating pool of amino acids. A certain percentage of any protein will pass undigested into the hindgut.

As we strive to provide a balanced diet for our horses, the requirement we are working to fulfill is for amino acids, not proteins. A good quality protein will provide the necessary amino acids in the correct ratios to meet the horse’s needs.

Essential amino acids explained

There are 22 primary amino acids and 10 of those are considered “essential.” Essential amino acids are those that cannot be synthesized by the body in adequate enough amounts to meet the demand; they have to be provided in the diet. The 10 essential amino acids are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.

In order for a protein to be synthesized, all the necessary amino acids must be present at once. The amino acid whose supply runs out first and “limits” protein synthesis from proceeding is considered the “limiting amino acid.” For horses, lysine is the first limiting amino acid. In other words, it is the one most lacking in the equine diet; therefore, it is important to supply adequate levels of lysine in your horse’s diet. Growing horses, third-trimester broodmares and lactating mares have the highest lysine requirements.

Protein source is important

Since lysine is the first limiting amino acid in the horse, the protein source utilized in the equine diet should be high in lysine, especially for growing and reproducing horses.

• Soybeans are high in lysine and historically have been the ingredient of choice when formulating a good quality horse feed
• Soybean meal (the high protein part of the grain that has had the oil removed) provides excellent lysine levels
• Canola meal (not to be confused with rapeseed) is another source that provides adequate lysine for growing horses
• Animal sources, such as milk proteins, can also be considered
• Grains and grasses are typically low in lysine

Other sources of protein

The follow sources of protein can be found in equine feeds and supplements. Although they do provide lysine, they typically do not provide adequate levels for growing or reproducing horses.

• Cottonseed meal
• Linseed meal (not linseed oil)
• Brewers grains
• Distillers grains
• Alfalfa
• Corn gluten

When you are reviewing your horse’s feeding program be sure to check out what source of protein is provided by your feed. It may make a difference.