I don't know deer, but cows get it from meat [1] > Cattle are believed to have been infected from being fed meat and bone meal (MBM) that contained the remains

I don't know deer, but cows get it from meat [1] > Cattle are believed to have been infected from being fed meat and bone meal (MBM) that contained the remains of other cattle who spontaneously developed the disease or scrapie-infected sheep products. The outbreak increased throughout the United Kingdom due to the practice of feeding meat-and-bone meal to young calves of dairy cows [1] https://en.wikipedia.org/wiki/Bovine_spongiform_encephalopathy#Cause https://en.wikipedia.org/wiki/Bovine_spongiform_encephalopat...