Corn is considered a heavy grain because it is denser and higher in energy per unit weight compared to oats. Oats, corn, milo, barley and wheat are energy feeds. Protein sources include soybean meal, linseed meal and sometimes, alfalfa pellets. When compared to soybean meal, linseed meal is a lower-quality protein as it is low in lysine. Most grains, however, have adequate protein to meet the needs of mature horses, either idle or working.
Grains are also high in energy, so they can meet the energy needs of any class of horse.
Therefore, most grain rations have calcium added to maintain a balanced ration. Because grains vary considerably in density, feed according to weight, not volume. Always weigh your feeds. There are many excellent commercial feeds available that are balanced specifically for horses. Some horseowners prefer to mix their own rations, rather than purchasing commercially prepared feeds.