I have hatched two batches of meat type birds that I obtained. One batch of A&M and one batch of another variety. I have hatched several bird before from other sources and they are always crowing and laying by 5 or 6 weeks of age. These two batches are now 8 weeks and only two A&M males are crowing and only two hens are laying. None of the other variety have even crowed. This is out of about 70 birds total. I keep them under lights 15-16 hours a day. How much longer should I wait before being concerned? What am I missing here?