I have never owned one of those being marketed as "Heritage Whites", so can't answer other than they look pretty meaty in the picture.
The CX have to be kept on severely rationed, lower protein, grain based feed [I use commercial crumbles] to get them to breeding age. They can have all of the grass or other browse to eat as they want. It remains to be seen how healthy the crosses to an Ameraucana will remain. I'm hoping the slender Ameraucanas, a lean breed, will reduce the amount of fat I've always found in the mature CX's body cavity when I've butchered them. The fat makes them a great tasting stew hen, but not so great for their own health. The major health problem with CX, in my opinion, is their bred-in tendency for putting on fat. Cockerels could be used to cross breed, if kept small enough. In the commercial breeding programs, they live breed the parent lines by using restricted diets, and the cockerels often have to be replaced by younger ones. The females are spent and culled after their first year. These parent lines, not available to us, still have a short life before their lowered productivity and livability make them too expensive to keep. The chicks we buy are the terminal generation from crosses of 4 parent lines, and were never intended for anything other than slaughter at 7 weeks of age. Many individuals here are holding them to 8 weeks or longer to get larger broilers, but that is when the health problems start to surface.
My Ameraucana X CX crosses are being raised on free choice, 22% crumbles for maximum growth rate. So far they are healthy, though they can not handle heat as well as my other birds. The full feed diet is to test both their growth rate and livability. I have not kept tract of their weights, but know they are much bigger, faster growing, and carry far heavier meat than anything fed with them. They could be processed at 2 months of age if I wanted a small but fairly meaty carcass.
To breed the CX pullets, I have to feed them separately from the others, otherwise the CX eat too much and die. Cockerels or cocks from other breeds must be removed from a breeding pen of CX pullets and fed back up to keep them healthy. Since a chicken stays fertile from a single breeding for several days, this is really not a problem, other than the extra effort and pen space needed. While I can't pen a bunch of males together, due to serious fights when one is put back after being used to breed, and I don't want to have to keep separate pens for each male, I can just pull a male from his regular breeding pen and put him over the CX for a couple of days; for maximum fertility I can use a few different males in rotation, and return them to their regular harem with heavier, higher protein feed. This can keep the CX under a male at all times.
