I have a Rhode Island Red,Red Comet, Leghorn and an Australorp hen. All have given me equal eggs in a clutch, but the Australorp eggs are the only chicks I can hatch, all the other chicks die late in development, they never even pip. The Australorp chicks hatch with no issues. I follow the book on incubation temps, humidity,and turning. Why is this happening? The hens eat the same diet, are free range and only 1 rooster. The only difference in laying, is the Australorp hen will take her time laying... literally hours, but the other hens are more of a sit and ditch layer. I can't figure it out!