Right now he is on a "custom" sweet feed that my barn owner has. He used to be on Purina Strategy. He eats a tim/grass mix all day long. As for the ability to exercise? I'm not really sure what you mean. He is ridden about 4 times a week.
I think he probably developed the habit two owners before me. The girl that sold him to me saw him in a field while passing by one day. He was very skinny (I saw pictures and it was bad) and not taken care of. One day she and her trainer stopped at their house and asked if they could take the horse to a better place. The woman said that it wasn't her horse, it was just in her field. So she did some calling around and eventually she got him to her farm. He got fattened up pretty well and she had started his training process. She had him for a year before I bought him. Before she found him, I have no idea what he had to go through. It makes me so mad that you can just look at a horse everyday and not even think about feeding it or finding it a better home.
Some horses crib out of boredom as well, which is why I was wondering how much room he has to roam and how much exercise he gets.