I have a few older hens that were laying fairly well until we added some pullets to the flock. Now they have shut down completely. It started with a few rubber eggs and now nada. We have tried oyster shells. Our younger hen still lays though. Any thoughts? Can older hens, 2 to 3 years old, just putter out and never start up again? They are all golden comets and RIRs and have been integrated for three weeks now.