My hens shells are weak and occasionally misshappen. I have offered them oyster shell, but this has not helped Do any of you mix them in with their feed? Can you overfeed oyster shells? Could they need something else? They are fed layer pellets. I have looked up diseases that cause weak eggs, but my hens have no other symptoms. I have heard of egg drop disease, but so far that only exists in foreign countries. My hens are only a yeAr old. Does anyone know what else I could try? Thanks!!