Its been a week or two ago now but last month I set 72 eggs for a friend of mine. Come hatch day only 32 hatched, I was suprised because I had other eggs in the bator that came from my own chickens and I had a 90% hatch rate on those and they were all set the same day. I took the unhatched eggs out of the bator after a week and cracked them, ALL were fully developed! What could have happend, she feed Purina for her laying hens and I know Purina fortifies the feed with calcium for stronger shells... could the shells have been to hard for them to pip?? I have no idea, but I was just looking for suggestions because she gave me 72 more to hatch for her and if it was something I could fix then I would!! I have an redwood bator, eggs are turned 3 times daily manually. Temps stayed right, no spikes or anything. All but 3 of the eggs were fully developed, the 3 that werent were just ones I missed when I candled because they werent developed at all. These chicks are red sexlink, black sexlink crosses.