Bec, it sound like you did everything you were supposed to do. I read the symptoms of Newcastle's and it doesn't really sound like what's happening with your birds. I've never seen the disease first hand, though, so I'm only going by what I've read.
I'd be more inclined to think vitamin deficiency, or some sort of toxic substance, maybe from a contaminant in the feed or environment. Is there anything they might be ingesting that could cause a problem? They'll sometimes eat things you wouldn't expect them to have any interest in. Styrofoam, insulation, all kinds of inedible stuff.
How long until they give you the test results?
I'd be more inclined to think vitamin deficiency, or some sort of toxic substance, maybe from a contaminant in the feed or environment. Is there anything they might be ingesting that could cause a problem? They'll sometimes eat things you wouldn't expect them to have any interest in. Styrofoam, insulation, all kinds of inedible stuff.
How long until they give you the test results?