My girls are 14-16 weeks old now and after finishing the final amount of grower feed I plan to switch them to layer rations (Layena and Dumor brands). What I am curious about is if this may be too early for their kidneys to handle the extra calcium. When do you ideally want to begin free choice oyster shell for them? I have heard that you want to wait for the first egg to be laid and also that you should introduce it earlier, before they lay. Any ideas? Thanks!