I have 7 laying pullets, almost hens. All the same age, and get the same feed. 2 white Leghorns, 1 Easter Egger, and 4 Isa Browns. It seems, for the last couple of weeks, every Isa Brown egg I crack open, the yoke breaks open right away. Just the Isa Browns. The first 600 they laid were fine. They've never had the amazingly thick shells my Leghorns and EE does. Is this just to be expected by a hybrid of the machine gun egg laying type?