I just got two chickens from a friend: a Black Star and an Isa Brown. They are 7 months old and haven't started laying yet. When I picked them up, I realized that they were only feeding them cracked corn and grit. The chickens were free ranged until a fox got four other member of their flock, so the previous owner recently built them a shelter and run. Would their food be what's causing them not to lay? The stress from the fox? How do I get them to start laying?