Are you providing them with crushed oyster shell, and are they eating layer feed? I would recommend purchasing some crushed oyster shell to supplement their calcium intake. Or, grind up some clean egg shells into a powder and feed them that. I use a coffee grinder to create a kind of eggshell powder, and then sprinkle it on their feed. Make sure that you aren't feeding them too many treats, as that will unbalance their nutrient intake.