ruminants have multiple stomachs full of bacteria that produce plenty of B12. that is why beef is so high in B12. however, very little bacteria can live in a human stomach because of its high acidity. thus all our B12 producing bacteria live much further down the digestive track, too far down for us to utilize the B12.
wild animals often get their B12 from eating dirt and/or feces that contain B12. so if you want to do that, fine.