Proteins play a very important role in the body's functions. They are needed for the formation of cells and the construction of new tissues. Most of the hormones that regulate the body's metabolism and digestive enzymes are proteins in their structure. Proteins cannot be stored in the body as such, but the part that the body does not need to form its own proteins is converted into energy, just like carbohydrates and fats.

Amino acids

Proteins are made up of amino acids. There are about 30 amino acids in total. Their mutual occurrence and order determine the nature of the protein, just as the end result of building with Legos is determined by the number of Legos available. By joining together in different ways, they can form an enormous number of different proteins. When proteins from feed are transported through the digestive tract, they must be broken down into smaller parts before being absorbed into the bloodstream. This mostly happens in the small intestine. Eventually, after the amino acids are absorbed into the blood, they travel to the part of the body where protein is needed. There they are recombined and are used to make, for example, muscle or hormone protein.

Limiting amino acids

The body's proteins are completely defined by their amino acid composition and mutual arrangement. If even one of the amino acids needed, for example, for muscle protein is missing, protein cannot be formed. In this case, all other amino acids are unnecessary and transferred to other uses in the body. The situation can be compared to making pea soup: if peas are missing, it is difficult to make or eat pea soup and it is difficult to make any other soup from the other ingredients.

The amino acid that determines the formation of protein in this way is called a limiting amino acid. Even a small addition of this limiting amino acid can cause a clear increase in the formation of protein. In horses, the limiting amino acid is most often lysine, which is especially important for growing foals. Other amino acids that are important for growth are threonine, methionine and tryptophan.

Essential amino acids

Fortunately, the body can convert some amino acids into other amino acids when needed with the help of carbohydrates. Almost half of the amino acids are those that the body cannot produce, and must be obtained as such from feed. These amino acids are called essential amino acids.

There are ten essential amino acids for horses:

• lysine
• methionine
• tryptophan
• phenylalanine
• threonine
• leucine
• isoleucine
• valine
• arginine
• histidine

Generally, horse feed contains enough of these amino acids and in practice, there is usually no deficiency except for lysine and perhaps methionine. Important amino acids for racehorses are also leucine and valine, which are needed for muscle function and energy metabolism.