[wodenokoto]

That's pretty much how we got Mad Cow Disease [1]

    A British and Irish inquiry into BSE concluded the 
    epizootic was caused by cattle, which are normally 
    herbivores, being fed the remains of other cattle 
    in the form of meat and bone meal (MBM), which 
    caused the infectious agent to spread

[1] https://en.wikipedia.org/wiki/Bovine_spongiform_encephalopat...

[bduerst]

They were giving the cows feed that was salted with protein sourced from ground up sheep, of which there were trace amounts of neurological tissue containing the prions.

It's not unusual for farmers to add amino acids as a supplement to feed. It's one of the targets for high-nitrogen (amino acid) GM corn.