Chickens (like other birds) are going to lay eggs. I am not aware of anything one can feed them to discourage egg laying. It is a process that has gone on for millenia, from the dinosaurs on down, and things like hens becoming egg bound, will just be something you as their caretaker, will have to handle. There is a wealth of information, wisdom and experience on these boards, and if you should have anything bad happen, I am sure you could manage quite well.