If your horse is being lightly ridden or has a tendency to gain weight quickly, hay or grass pasture may be all it needs. Good quality hay and grass has all the vitamins, protein, fiber, energy and minerals a horse requires.
If your horse is carrying a foal, nursing a foal, working hard, or has difficulty maintaining good condition you may want to add grain or other concentrates to its hay or grass diet. Growing horses may need some grain or concentrates as well. Young horses need to be fed carefully, and over feeding avoided. Over feeding and too rapid growth can cause abnormalities in a young horse’s joints.
Feeding over 5 ½ lbs (2.5kg) of grain or concentrates per feeding substantially increases the risk of colic. Horses fed over 10lbs of grain a day should have their meals divided into 3 or more smaller portions.