Can i get some help?

I own a 20 year old pony of america (POA) and i'd like some advice on feeds that keep him strong and healthy in the winter. He has constant access to pasture and barn but he used to be very ill with heaves and so doesn't eat much hay. He's smart like that. And i also ride him at least 2 times a week, if not more. I need some feeds or activites or something to keep him in shape. Well, thanks for your time!
cya!