I agree with others, basically. BUT if he's on grain/sweet feed, while it might not be 'broke' now, they're still a common cause of a number of health problems, so I'd avoid / minimise these ingredients.
Also it depends on your feeding regime - not just what & how much you feed, but how often & what size meals. Horses are designed to eat little & almost constantly throughout the day/night, of low grade(compared to conventional practice) fibrous feed. That's generally the best way to manage feeding - free choice hay / grazing, and if you're going to hard feed, make sure it's in tiny meals, at least 3-4 meals per day.