you can keep them indefinatly just restrict their feed(i hav let mine free range so they have to work out too) , i also put asprin in their water so it helps them with their circulatory system. not too much and not all the time but once or twice a month ill crush a few up in their water. they dont like the taste very much but they drink it esp since its the only option lol. mine are healthy 4months now but i kept them for a year and a half too and when i finally butchered them i got a dressed bird of 15 lbs. thats a lot of chicken