I feed my horses complete feed as well and I let them have free choice grazing when out on pasture or I keep a bunch of grass hay in front of them to keep them chewing and busy. They're healthy, happy and nicely round. I would not feed a hay like alfalfa, oats, rye, something that's either high protein or high carb though, I'd think that would be in the danger zone. Bermuda or prairie hay....not a problem. And of course I also feed them salt, 1 oz/twice a day or give them a salt block depending on if the horse likes the block or not.