A natural source of calcium. A must before and during breeding season. Especially important for the hens in order to produce smooth, hard shell eggs. If the grit you use does not contain oyster shell, we suggest you add some. A good pigeon grit may contain as much as 45 percent oyster shell. The loose crushed oyster shell may be used by itself in small containers or add to your grit. Please note: the size of the Oyster shell is SMALLER than it used to be. Crushed Oyster Shell 50 LBS.