Well, I suppose it does depend on the horse...I've actually read that drafts have a slower metabolism than some of the lighter breeds and that they sometimes require less food as a result. I suppose it depends on the amount of activity the horse does. An idle draft horse may not need much of a different amount than a regular horse...
However, I'd say in general, expect to pay for more food when dealing with drafts.
Because my girl is a senior, I do have to put a lot more food down her way to keep a nice appearance to her. Even as an idle horse, her food demands are large...
By the way, that belgian boy is just gorgeous!!!