Feed about 2 pounds of hay per day for every 100 pounds of body weight. Feed hay by weight not flakes. Young horses, horses in hard work, pregnant mares, and mares with foals usually need grain and supplements. Corn has a very thin covering so does not provide much fiber but provides twice the energy content as the same volume of oats. Commercial feeds come as pellets or grain mixes.
Pellets can contain both hay and grain.
Grain should be fed by weight, not volume. To avoid competition, fighting, and unequal rations, feed each horse individually. If a horse gobbles his grain, it can cause choking, inadequate chewing and poor feed utilization. To slow him down, feed hay first, and then grain. Add golf ball sized rocks to the grain and use a large shallow pan rather than a small, deep bucket.