Cows are vegetarian, as are deer.
> 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_encephalopat...