Oyster Shells for Chickens: Benefits, When to Feed, and 6 ...
#2 Crushed Limestone. Contrary to what some marketers would say, crushed limestone is not considered insoluble grit but rather a great source of calcium. In fact, it is also being as one of the active ingredients in some layer feed. Also, crushed limestone is believed to be having only 33% calcium while oyster shell has 34.3%.