I had corn described to me by an ex horse racer:
"Corn gives them (horses) energy. Give them the amount they need for the energy they will use. If they have too much energy and sit in a stall, they just go nuts, trying to use that energy and not being able to. They can get founder, colic, all sorts of things. If they get out and play enough, they work hard enough, corn is a good thing, it'll keep em going."
My chickens have an acre and a half to roam and there's only four of them. They get a handful of an oat/cracked corn/BOSS mix scattered near their run each day. They're doing great. Granted chickens are not horses, but the concept is the same. It doesn't just raise body heat, it gives lots of energy. I also noticed that the chickens will leave behind some of the grain mix if they are in the mood for more bugs or greenery. They make decent choices.