what are you feeding them? Did you dip their beaks in water and provide plenty of it in accessible containers? Not much should go wrong with chicks. Food, water and heat. That's the big 3, and if you managed those items I'm at a loss.
sorry you had such a time.
I tractor them. Shop around and buy the cheapest chicks I can get and do a group buy with friends that raise meaties. Feed cost $13 for 50 lbs. Process them weigh and divide total pounds by feed costs.
They're still & only chickens. Same requirements as "normal" chickens so you should be fine.
To discuss what breed to get, depends what you like. Do you want healthy, meaty birds in 8 weeks? Or healthy birds in 12 plus weeks? Standard breeds can't hold a candle to CX for meat production...
I cool mine off on ice immediately after processing. Then after their core temperature is cold! I package in shrink bags and freeze. Never had any complaints about toughness.
I have let birds rest for three days after processing, and the frozen the same day ones are just as tender.
Lets face...
I have since upgraded the tarp to several sections of corrugated vinyl, light weight and cheap. Food is dry and their water is along the opposite side. It is 2x2 heavy wire covered in 1/2" hardware cloth. Wheels front and rear. 7'x14' and I house a max of 30 birds. good luck and enjoy.
Odds are better if you grow them big and fast. You can be certain they will have issues as they get older. So, get them to the desired weight quickly and take them to freezer camp!
Good luck
About all you can do is restrict feed. They are on track with the weight. Good luck
Than again. What's wrong with getting them huge and killing them early? A week early is a good thing with these birds. The longer they live and the more you move the tractor the more risk of injury and...
I use 19% locally ground mash start to finish. Process @ 7-8 weeks 6-8 pounds. Cx'ers by the way. Chicken meat is not marbled so feeding corn to "fatten" them up is not worth the time or money.
All good