Chickens eat their own poop! 
So did Hitler, too, although he didn't know it: His personal doctor made him these "special strengthening pills" into which he mixed some of the contents of old Adolf's potty as a silent protest.
In fact many animals eat their own poop, or actually each other's, to keep their stomach bacteria alive and kicking. And to create you a bad case of food fear: Have you ever thought that grain, your daily bread, gets its growing power from fertilizers, which actually are...