Keep in mind that chickens are not stupid. They are smart enough to be chickens. That is to say, smart enough to keep the species going. I've said before and no doubt will again, that if chickens were stupid or careless enough to eat toxic plants, they'd be extinct by now. Ours range in areas...
Truth! If it's edible they will eat it to death. If it's not edible they will scratch and waller and dust bathe in and around it until the plant surrenders in despair.
Oh wait. There's an exception. Several years ago we planted dozens of lilies given to us in tight rows and when they came up...