I just found out that my boarding stable has been offering my horse a complimentary turn out service while I am at work all day. They started turning the horses out on very lush pasture for up to 12 hours a day. He has been turned out a few days in a row now with a LOT of grazing time. At the barn I used to keep him at, he never got any grass, only hay. He's a 16 hand TB, healthy weight with no history of founder. But, like any worried horse mom I kind of freaked out when I found out he's been grazing so much while I am at work. What are the chances he can founder? What should I look for? Thanks!