Remember "Mad Cow disease"? It's a prion disease as is Creutzfeldt Jacob disease, Chronic Wasting Disease in Elk, Deer and Moose, scrapie in sheep, etc
see the CDC page on prion diseases---or the book! https://www.cdc.gov/prions/index.html Turns out that feeding animals "protein" from their own breed is a BAD idea and actually a lot of cross species transmission is known to happen----vegetarian animals should be vegetarian!!!
I was always upset when the restaurants would only serve beef "Well Done"; it needs to be over 700 degF to deal with prions so that was just trying to fool folks that it was safe. I like my beef rare and am willing to take the chance knowingly.