Have you considered cutting their feed with oats? You want something that is a filler but won't make them fat, so corn won't be the answer, although corn as part of their diet may be necessary. When we want to keep weight down on rabbits that have a tendency to get fat on us, we give them timothy hay, but I doubt your chickens want to eat hay. However, the hay cubes when wetted might be good. That can be more expensive and a hassle than it is worth to try though.I picked a smaller rooster when I picked Bert. I want the CX body style in my future chicks. Bert made it 11 months. I think Bert Jr may be my answer. He has the large breast on a taller frame. Breeding him back to the CX hens could give me the meat birds I want on a larger frame and huge dark meat areas.
I am hoping I can keep 3 of the 6 hens alive to lay in the spring. I will be cutting back on feed even more next week. I will take them off the 15% grower. Not sure what I will use.
I am setting up for CX's in March next year now. I think I will buy all roosters and order a handful of hens only.