Oyster Shell is a premium source of calcium for building stronger egg shells. Provide to laying hens around 20+ weeks of age. Oyster Shell is rocks with nothing added. Specifically, 100% natural limestone. Oyster Shell is a blend of fine and coarse untreated calcium carbonate (CaCO) mined from limestone. Fine particles provide an immediate calcium supply while coarse particles provide a slower, steady calcium release. A mix of fine and coarse provides a consistent calcium release into the hen’s bloodstream overnight providing strong eggs and stronger bones. Eggshells are 94-97% calcium carbonate. Oyster shell is an organic, natural way to give chickens the calcium boost needed to produce strong eggshells that will not break. Stronger Eggshells: Get stronger, thicker, healthier eggshells from laying (20+ weeks) chickens by boosting their calcium with oyster shell organic, all-natural calcium booster