For what purpose are mollusk shells crushed and added to poultry feed?

The shells of molluscs are composed of calcium carbonate, the same substance that makes up the shells of eggs in birds. Poultry are encouraged to lay eggs all year round, not just during the breeding season. But in order for the birds to fly, in addition to normal food, a large amount of calcium carbonate is required. Therefore, it is added to the diet of birds in the form of crushed shells of used eggs, pieces of chalk or crushed shells of molluscs.
In the acidic environment of the stomach, this substance dissolves, enters the bloodstream and is used.