I acquired three, two year old Sexlink hens in September. Two of them died. One from unknown reasons. The other was egg bound. The third and lone survivor yawns quite often and shakes her head. I suspect that she has gape worm. She has never laid an egg for me, but does sit on the nest. Can gape worm affect egg production? I recently added four more hens to my flock. Should I treat all of them for gape worm?