No Animal or Plant makes it... only bacteria and yeast. Every animal in the wild is healthy and happy. Some animals eat animals which is natural and possibly thier source of b12.... however most animals don't.
How do the animals that dont eat other animals get thier b12 if thier own bodies do not manufacture it, especially when it is such a necessary vitamin to life?
I would think that the yeast/bacteria that make it... would be somewhere in the animals bodies, where they could easily absorb it. Especially since the meat in cows and such are full of the b12. A reliable source... and that spot in my opinion would be where all the other yeast/bacteria are... the bowels.
P.S. more meat eaters wind up with b12 deficiencies than vegans each year.