Why do chickens eat?

@Kevin Stickney In theory, yes. You could offer feed and oyster shell, etc., and they would balance their nutrient needs. The practical issue is that birds invariably take too much oyster shell because of its novel texture. We see this in small flocks where a calcium feeder is set up. Birds consume 8-10g/d of oyster shell and then soft shelled eggs appear because of an induced P deficiency. You could give two diets, High and Low in Ca, and they would balance themselves, but that becomes a logistics challenge. A pre-lay diet with most Ca as large particle will work, assuming it’s a mash diet.