You need to slow the growth rate by limit feeding. You allow them access to full feed for the first four weeks. I intensively weighed the chicks every other day. I selected the two best doing cockerels and two pullets. At four weeks you weigh the feed out per the weight chart for Broiler breeders and feed the appropriate amount of daily feed. This goes on following the weight/age/feed amounts until 16 weeks of age. At this point they begin to sexually mature and must be slowly increased to a higher amount of feed to mature. The bone structure is there, the frame is there, and most importantly the internal organs do not have to play keep up/catch up. But I still lost both of my cockerels upon maturity. Both died within days of each other. Both died of the same symptoms. Blue comb and gasping. Heart failure due to Roostering at 21 weeks of age. The pullets came through it just fine and started to lay at 23 weeks. One hen just got fatter and fatter. She never did lay many eggs so I culled her and kept the better hen "Betty White".
