I have 6 chickens and they range from about 17 to 20 weeks. None are laying quite yet but at least one has started to squat some. They are still on grower's feed and I still have about a half a bag left so I am wondering if I need to put out oyster shells out for those who will start laying before I finish this bag out. I went to the store where I got the feed and they said it was okay to wait until at least 50% of the flock were laying before making sure they had calcium since the first eggs aren't great regardless if calcium was available. What do you all do?