Cattle don't need flora to digest grains. They never ate grain in their evolutionary past, only grass. Their flora doesn't process it- which is why E. coli take

Cattle don't need flora to digest grains. They never ate grain in their evolutionary past, only grass. Their flora doesn't process it- which is why E. coli takes over. The majority of cattle which end up in a grocer, convenience store, or restaurant spent most of their life completely infested with E. coli. Right up to the point of being thrown into the grinder.