Coarsely ground or broken seashells, Shell grit is used by birds as a source of calcium to harden the egg shell ...and to aid digestion... Designed to help chickens’ digestive system function well and break down food. Other uses include protecting plants from slugs or snails and in aquariums. If chickens are able to free-range, they should be able to find enough grit on the ground to peck at to satisfy their digestive system requirements. However, adding shell grit/ground up egg shells to your chickens’ diet is a great way to keep their calcium levels up. If your chickens are in a coop run or fenced enclosure, it is recommended you add grit to their diets as they may not be able to forage enough naturally.