Have you read any of the old poultry magazines and books from 100 to 200 years ago?
First off those folks tried any and everything on their birds! There losses were no higher or lower than ours today.
I'm with Fred. My cure for most any kind of disease is to kill it. It's fast, effective and cost very little. One year I killed over 75% of my fowl when fighting Coryza. I won!!
Now as to preventives, that is a whole different ball of wax. I'll try and use most anything!
Read those old books; they all suggest preventives. Some of their thoughts would make these moderns squirm!
An example: Ground glass was fed for worms.
Arsenic was used for about everything and anything.
As for preventatives, I'm all about that as well, though not much on anything that couldn't be found in nature...ground glass not being one of them. But arsenic? In every green apple seed that is eaten from our orchard when the trees do a natural culling in the spring. I've never seen a chicken just eat around the core on those. Not that I would buy arsenic and feed it to the flock, but they can find that in nature enough.