A friend of my son’s moved away and gave son a pair of chickens rescued from the meat farm. These things were morbidly obese and could not even climb up the ramp into the coop. One just dropped dead one day. The other became so pathetic and torn up by the rooster that both were dispatched.
They’ve been bred to grow very fast and they have to be harvested by a certain age or bad things will happen. I thought 12 weeks was quick but another poster above-Pollard (#42) says one certain breed takes just 6 weeks to mature.