Proteins are made up of amino acids, including lysine, the most important amino acid for growth in young horses. Diets for growing horses must include lysine levels of .6 - .7 percent of the total diet. Minerals are present in very small amounts and are absolutely necessary for growth and the functions of the skeletal system, blood and the body's soft tissues. Calcium and phosphorus are the two most important minerals for skeletal development and maintenance. There should never be more phosphorus than calcium in horse rations.
Salt aids the body in fluid and temperature regulation.
It is vital for horses to have salt available, either as block, loose or mixed in the feed in the form of trace mineralized or iodized salt. Most grain mixes contain between .5 and 1 percent salt, sufficient amounts for most horses. However, pastured horses or those which do not receive a concentrate mix containing salt must have access to free-choice salt. Most vitamin requirements are supplied by the forages and grains in horse diets, although it is often standard practice to include a vitamin premix in horse diets. A many be needed for horses during production and growth.