Would this be worth a try to add to chicken feed? Whenever you use eggs, save shells. Wash shells out right after using the eggs and save them up for about a week or so until you have a "batch" worth processing. Bake shells at 350°F for about 8-10 minutes to remove the mineral oil coating and make them brittle enough to grind. Grind to a fine powder in a food processor, blender or coffee grinder (I use a coffee grinder). Make sure there are no sharp, gritty pieces. 1 tsp. of powder supplies about 1800mg - 2000mg of calcium.