One chicken owner says she feeds all her chicks, juveniles, hens and roosters starter feed as a steady diet (so the roo and non-laying chicks/chickens don't get extra calcium from the usual layer feed) and then she leaves oyster shell separately at-will for the laying hens that want the calcium. That way there's not too much calcium concentration as found in layer feed and only the laying hens will eat the oyster shell nutrition they need during their laying cycle. Roos, juveniles, and non-laying hens usually ignore the oyster shell/calcium carbonate but hens will consume when they are ready to start laying. If layer feed is the only feed offered it is too much calcium concentration for pullets, cockerels, roos, or for hens that have a calcium spotted egg shell. Offering non-layer starter feed and having oyster shell at-will is the way one chicken owner solved her calcium-spotted egg shell problem. For my little flock I offer Turkey grow/gamebird feed, and unprocessed layer feed, and layer pellets, and oyster shell at-will, and calcium carbonate at-will. I have some old hens that don't lay so much any more and new pullets newly laying so I have a variety of feeds offered for them according to their different nutritious wants/needs. They pick what their body needs the way they do when they naturally forage on their own. Animals seem to have an instinct about what nutrition their body needs. Hope this helps some!
