When he was a child???? How long ago was that? Why are there even any cattle left at all?
They were eradicated in the 60s and 70s by the USDA station in Mission, Texas dropping boxes of lab bred screwwords from airplanes. The flies had been (mostly) sterilized by irradiation. Over the years of the wild females breeding with sterile males their population declined and eventually the program ended.
I remember doctoring them with my Dad too. The female flies lay eggs in any blood or scratch on the animal. (Including castration wounds and earmarks, newborns’ umbilicus and around the tail.)
It affects everything else too, not just cattle. I’ve seen sheep, goats, deer, racoons, and heard of the occasional human. I’m sure the homeless population will be getting them if we go back to those days.