Most mature pleasure horses doing light work need only the nutrients supplied by good quality grass or alfalfa hay. A good starting point is 1.5 percent of the horse's body weight divided into two or three meals daily. For instance, 5 pounds of hay (1 flake) should be fed three times per day to a 1,000-pound horse. This percent can be decreased to 1 percent for second or third-cutting alfalfa hay. Use this only as a guide.
For more information, please read the story Eating Lots of Hay is Vital to Your Horse