Studies of commercial flocks have shown caged birds to be the healthiest. Insects, worms, wild animals and birds, can carry bacteria on their feet, bodies and fur, and in their droppings and saliva. Sharing ground, eating them, and eating or drinking from the same reservior can play a role in fowl cholera, pox, infectious bursal disease, mareks and probably many other diseases. I would think may also be more likely to get into natural or created toxins/poisons. Having said all that, I still like to give them a little free run time every couple days.
As far as predation, that just depends on where you live. I have coyotes, dogs, hawks, birds, raccoons, skunks, and bobcats. I have to cover my pens with chicken wire, twice on the sides and once on the top,and bury it 6 inches into a trench, followed with fence post cement and a base board. A neighbor had a bear tear the door off his henhouse. After he replaced and reinforced it, the bear came back and tore the siding off. He's out of chicken raising.
yes,Dirt Farmer, you are correct. BUT the key here is "commercial flocks".... as in those large factory farms with flocks of hundreds, or sometimes over a thousand birds per building. But if you are talking about small sustainable farms raising heritage breeds of poultry then the finding of these "studies" do not apply.
We raise only heritage breeds here on our farm, and they do better on pasture than in confinement. We raise them all natural & in smaller numbers than tose commercial operations, and they are moved to large pens & allowed out on the pasture starting at age of 5-7 weeks old.
We do vaccinate for Mareks & LT as those are 2 diseases common to our area.
As for predator control we use 6 ft. high fencing around their whole pasture & have 2 livestock guardian dogs, a Great Pyrenees & a Belgium Malinois. .As long as the chickens stay INSIDE the fence line they are safe. Birds that habitually fly over the fences?? I usually start naming them "fox bait."...... LOL
Just as there is more than one way to skin cats, there is more than one way to raise poultry. It all comes down to what breeds & method works best for you & of course what the intended purpose for your flock...... personally, the welfare of my chickens is my main concern. I have used just about every system there is and this is what works best for me.... pasture raised, grass fed chickens are happier & healtiher chickens, in my book....