if you get lots of defects its probly a genetic thing (inbreeding) last year my pens got mixed up and for several generations they were all just inbreeding too close. On my last hatch i ended up with tons of cross beaks, crooked necks, messed up toes and one with a bizzare swollen joint. I slowly culled them all out, they were for the table anyway. The crooked neck i think is hereditary and just exacerbated by inbreeding, because my first one came from two unrelated parents, but she's happy and lays eggs so she's staying out of the freezer for now.
*all my crossbeaks had the same mortality rate as the others, they seemed perfectly normal and healthy ezcept for their beaks.