I do not feed any grain or horse feeds that contain grain products. They make my mare fat and my gelding hyper and skinny. I feed free choice quality mixed grass hay, alfalfa pellets, and a custom blended supplement from horsetech.com. I have them add all the major vitamins and minerals, extra magnesium (we're really low in it here and my mare is IR), extra biotin, a HIGH levels of Amino Acids (for good muscle and hooves). The supplement costs me $0.87 a day to feed, which is cheap considering what all it has in it. If I were feeding seperate supplements, I'd be in the $2-3 a day range.
I also give my gelding a joint supplement as he has an old injury. I use Equinyl Combo
I find my horses hold the weight better, have better condition, grow better hooves & hair, and have better attitudes on a NO-grain diet with proper vitamins. I won't ever feed a commercial horse feed or grain product again, if I can help it