First 6 weeks loss insuficient protein I suspect was your problem use 29% medicated gamebird turkey starter. Then mix 50/50 with chick starter to drop protein level so no leg problems eventually dropping to 21% by 3 months when move to ground. Move to wire after 2 weeks so not eating standing in poop. Worm with safeguard as soon as you move them to ground. Never had unexplained deaths in over 300 chicks doing it this way.