I live in Ontario, Canada and I have 53 chickens (38 meat birds) and 15 pet/egg layers. The woman at my local co-op suggested I try raising these Whiterock's as I have had very good success with my dual-purpose chickens & egg layers.
They seem obese & only stand to eat & then basically flop down. I know from talking to local people that they have been genetically altered (which I totally disagree with and duer to this I will never purchase them again) to grow quickly. I watch my dual purpose hens frolic happily outside & feel that they have a very good happy existence. I don't know if this is good to condone killing anything, but I believe quality of life is crucial!! I am wondering if anyone else has ever has any of these chickens and at what age did they send them to the butcher??

These are probably not white rocks, but Cornish X Rocks, which are the variety used to produce almost all our fried chicken these days. They are ready to go as fryers at about 6 weeks, and as broilers and roasters at 8-9 weeks. They are not "genetically altered" in the sense you may be thinking. They are a hybrid (cross between two breeds) which happens to grow and build muscle very rapidly. Move your feeders away from their heat source and water, so that the birds have to walk to get their feed and water, and remove the feed late in the afternoon or early evening so they don't eat and sit all night. In the morning they will be very hungry. Then put feed out for them again. Keep the water fresh and full at all times. Good luck.

Heidi, these are called cornish cross, or cornish rocks. They have been developed through intensive selection for rapid growth and meat production. They are not GMO's. They were developed several years ago by originally crossing white rocks with white cornish, though that initial cross will not produce birds like the cornish rocks of today. You are correct, these birds basically sit all day long. It is difficult to keep them alive past 1 yr of age, especially when faced with heat as we are right now here in Illinois. They were not developed for anything but slaughter. I would slaughter at 4-5 lbs for fryers, closer to 8 or 9 lbs for broilers. You can't beat them for quality of meat.
You can restrict their feed to make them grow slower, but they will still be overly heavy birds at adulthood. I have successfully done this and used the pullets for crossbreeding, but they still can't handle summer heat.