One of my hens always lay eggs with a hole or little cracks on the bigger end. Not all, but half of them are that way. I feed my flocks with chicken layers, give them treats like scrambled quail eggs, pumpkins, rice from time to time. Crushed egg shell once or twice a week. Other chicken eggs are not broken unless they are dropped from somewhere high. I don't think the egg shells seem brittle. This hen lays on a flat surface. I wonder how it is caused and how I can avoid it.