If your horse is stalled, so that he has no choice but to stand in the wet he produces, then a grass hay is a much better bet for maintaining foot health. Next on the grocery list is in the feed bag. If your horse is eating the equine equivalent of tube steaks and french fries, you have a problem. This sounds strange until you understand why. The cost of a bag of feed is directly proportional to the goodies in it.
Cheap feed has cheap ingredients.
But how the feed mill meets those requirements is up to them. Prices on these commodities change almost daily, and often so does the content of the feed bag. They will use the cheapest ingredient they can get to meet the label requirements. Many of the ingredients in cheap feed are not very digestible to horses. The end result is that you have to feed a lot of the stuff to get any results.