An eggshell is 94-97% calcium carbonate and if a laying bird's feed is not providing all that's needed, calcium will be leached from your bird's body to provide this need. In a single year, a hen will put about 20x the amount of calcium into her eggs than is found in her bones. Providing oyster shells to your hens will improve not only the eggshell quality but also the overall health of your flock by reducing the risk of bone damage, strengthening blood vessels, improving the immune system and overall bone and cardiovascular health. You can see why this supplement is so important!
There are several ways to offer calcium to your flock: DIY eggshells, crushed limestone, table scraps high in calcium, supplements rich in vitamin A, E, and D to help absorption, and commercially prepared oyster shell.
Oyster shells should be offered in a separate feeder as a free choice option for your hens once your hens are about 3-4 weeks from laying age. chicks, older chickens that are no longer laying, and roosters do not benefit from an oyster shell supplement. Too much calcium can also be detrimental causing issues such as kidney failure, leg, joint, and metabolic issues, and egg binding.