Quote: What are the protein and calcium levels on the feeds you are using? Look on the labels.
Keep the oyster and egg shells in a different container......don't mix it in with the feed.
It's hard to say if they will keep doing it or not, first you have to find out why they are doing it.
Evaluating the size of coop (feet by feet) and number of birds...as well as looking at their nutrition levels are the first steps.