Background info; 4 EE's, 2 BR's born about April 20'th, 2010. Both BR's have had big bright red combs/wattles for 2-4 weeks. They are all about 22 weeks now and no eggs yet. I didn't know that you should switch your chickens off of "Chick Starter medicated" feed by 18 weeks and start them on "Layena", or another feed made for laying chickens. I just figured you were supposed to wait until they actually were laying eggs to switch the feed. I also had not been offering them the oyster shells until yesterday, and in 1 day they ate about 2 cup fulls. I gave another 3 cups today. Since they only eat as much as they need, I would assume they were greatly LACKING the calcium they needed to be healthy enough for egg production, meaning THIS could be why they have been waiting so long to lay. Unlimited food/water is always available, so I will update this post if they lay very soon. It is funny to me that wild birds can lay eggs without oyster shells, but maybe there are calcium sources out there, or they just don't need as much as chickens. Hope this helps!