Once upon a long time ago-
When we raised turkeys on the range because we didn't know much about their nutritional requirements, for one thing, we also had disease problems.
We got blocks of whey, about 40# as I recall, packaged in a plastic bag within a carton, that carried the Kraft logo still used today. They were supposed to help with all sorts of intestinal diseases including blackhead and coccidosis. I don't recall of it being very effective and really think it was fed out of our lack of knowledge about turkey nutrition and diseases in those days. Much like the ACV fantasies many subscribe to today.
The stuff tasted really bad, very acidic. I know because one day, when I was not very old, one of the hired guys had apparently had enough of me and rubbed my face in the stuff. My father liked the guy. He was on the payroll until my Dad put me in charge of the turkeys on the farm. I changed him to unemployed within a week. My older brother was very grateful that I fired the guy who had by that time become his father in law.
Back when I was very young my grandparents fed milk by products to the chickens when the few hogs they had could eat no more. It was never thought of as of much value as feed.
Today science knows that with what little feed value for birds there is in milk products it is much better used in mammals.
As for turkeys droning in the rain- well I have raised more turkeys on range than probably all the people on this forum put together can even imagine. It is BS. Something used to "test the gullibility of city people" as my uncle would have expressed.