I switched my girls to straight grower feed...20% and no calcium...I've provided a small feeder of oyster shell and another with grit... I've seen zero drop in the level of both feeders... I probably crush about 20% of the egg shells and return to the run area for then to nibble on. they free range the back yard all day. I'm guessing they don't need any extra grit but would expect some oyster shell consumption.