One of the poultry raising books I bought mentions that grinding up washed/dryed egg shells, is a great calcium supplement, for layers. The book says if they are ground up fine enough, the chickens won't recognise them as egg shell, and so won't start in on the fresh layed eggs. I ground up about a dozen, with a mortice, and pestle, but have been hesitant to feed it. Anybody try this? Any problems??