In debates, the contra side often claims veganism can’t be good because vegans have to supplement B12 (appeal to nature), while the pro side sometimes claims that even carnists supplement B12 indirectly because the animals get B12 supplements.
I would like to find out to which extent the latter statement is true/relevant.
How common is it for the livestock industry to supplement B12? Does it only affect certain countries, animal species, farming methods, …?
And why does the livestock industry supplement B12 in the first place? Does it only get supplemented for the benefit of the human consumers, or is it required for the animals to live long enough for the industry’s goals? Or both, so more B12 gets supplemented than the animal would need?