Healthy chickens come from healthy sources; it's good to be paranoid about where your birds come from! Major hatcheries try hard to have healthy chicks, while 'random source' birds may bring is awful problems. That's one issue. If you have enough space per bird, and a nice dry coop, and feed a good diet, your birds will have a good life. Lice, mites, and intestinal worms will occur at times unless your flock is totally indoors at all times. Most of us have chickens in an outdoor environment, on dirt, exposed to wild birds, so parasites will happen, and have to be dealt with. Right now I'm treating for mites, ugh! Mary