Couple problems, right off the bat ...
First? Although I realize what one has will most probably be transferred by those managing/visiting the birds, it's almost guaranteed when you just put 'em all together. And, if you're goin' where other birds are? You're gonna suffer through many diseases, 'til you either run out of birds, or be most careful.
Second? If the affected birds are joining the free-ranging chickens, then you've no control over how much exposure they have to toxins, such as they would get from botulism, or from aflatoxins, or from algae, etc. I'm a big fan of lettin' birds be birds, but they've gotta develop some level of tolerance ... some breeds are more sensitive than others, although that's based upon my own anecdotal evidence, but -- as little as four maggots can carry enough of the toxins produced by botulism to kill some adult birds.
If you're feeding DuMor, by the way ... there's been a bunch of it recalled; some for aflatoxins, others for containing no vitamin D. Although Cargill, who was producing it, claims they 'voluntarily recalled' these feeds? They didn't do a thing, 'til the USDA caught 'em red-handed w/ the bad corn.
From what you've said earlier, in another post ... the curled toes, and walkin' on 'em? Still sounds like riboflavin might be worth a try, as it's quick to correct, unless damage has already been done to the sciatic nerve.
From: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/206930.htm
Changes in the sciatic nerves produce “curled-toe” paralysis in growing chickens.
Deficient chicks are reluctant to move unless forced and then frequently walk on their hocks with the aid of their wings.
Chicks receiving diets only partially deficient in riboflavin may recover spontaneously, indicating that the requirement rapidly decreases with age. A 100-µg dose should be sufficient for treatment of riboflavin-deficient chicks, followed by incorporation of an adequate level in the diet. However, when the curled-toe deformity is longstanding, irreparable damage has occurred in the sciatic nerve, and the administration of riboflavin is no longer curative.
