I have a silkie bantam that has a pretty defined "cycle".... Which has taught me a lot. Considering if broodiness should be a natural part of a hen's cycle. She lays 10-14 days then goes broody. I've taken eggs from her religiously. But something kicks in after that last egg in her cycle and she wants to be a momma! Lol. After the 5 th time now this year it's getting to be a pain. All broody hens are probably not this way of course but it gives you an idea. There's a huge broody hen thread on here with great info. I think fisher lady is pretty knowledgable on the subject. I've read that the pressure of multiple eggs on the breast can trigger the hormone... But I think genetics play just as big if not bigger role than the physiology of a clutch of eggs under the breast.