A common misconception is that those huge double breasted chickens get that way by use of hormones. They don't. Actually use of hormones on poultry has been illegal for at least 50 years in the US. The chickens get huge because of crossbreeding and hybridizing.
I raise a few chickens for eggs mainly but looked into getting a few meat chickens. The typical meat chicken is a Jumbo Cornish X Rock and is usually ready to butcher at 6-8 weeks. If you try grow them much past that they put on weight so darn fast that either their legs will break or they'll literally drop dead of a heart attack. They are a hybrid selectively bred to put on weight in shortest amount of time. No hormones needed.
Antibiotics are another story.
We use natural apple cider vinegar(with the "mother") in their water which works for us.
Another thing the processors do is they will inject their processed chickens with water and other ingredients (broth?). If you buy raw chicken and the the label has "ingredients" stay clear, you're paying for an adulterated product.
Here's a link about hormones in poultry: