In response to the above, corn is a high energy suppliment. When the energy is not burned it is stored as fat. This is not always the best approach. The ideal situation I've seen was using high corn suppliment to stallions. They had regular exercise that was necessary, but not the ability to run or work all of the energy off as to a reguarly turned out horse. They were not allowed large turn out - therefore, storing and converting the rest of the energy to fat.
Oh, and I wasn't being critical of anyone's responce! Just adding on.