Our meat chickens are a breed specifically reared to grow quickly, known as JA747's. We get them as day old chicks, all yellow and fluffy, and providing the weather is good, they go out on the grass from day one. They have a cosy shed with a heat lamp, but most of them prefer to be outside chasing flies and eating grass.
If they were intensively reared, they would be kept in a shed with not much room to move around and may be fed growth promoters. They grow so quickly that their legs are unable to hold their weight, and for the last few days of their lives, they often cannot walk around. They would be slaughtered at 6 weeks old.
Ours are free ranging where they get lots of exercise and eat lots of grass as well as grain, chicken food and other vegetable and fruit scraps . They grow more slowly and their legs grow strong, so they are able to support themselves. We slaughter at 10 to 13 weeks old, dry pluck them, then hang in a fridge for a week before evicerating. The hanging intensifies the flavour so the meat really does taste like chicken!