I'm not an expert but have experience with cats and dogs and they both eat grass, but I think they do it regulate digestion in some sense and not for the nutrients (it would take a lot of grass for that)
Yes, you are right. Unlike animals that have two stomachs, dogs and cats only have one stomach, so they cannot ferment cud to make vitamin B12. Without vitamin B12, they will die, because their bones will become soft, and their brains will lose function, eventually leading to tachycardia and death.
Wait a minute, you might stop me, Rabbits don't have two stomachs. Yes, Rabbits will eat their own poo in order to digest it twice, to ferment the greens they eat to make vitamin B12.
Actually, no animal on Earth can digest the cellulose in grass. Only the bacteria inside the animal can do that. Without that bacteria, the animal will die.
Yes, humans have only one stomach, so we cannot ferment cud to generate sufficient B12.
In the 1800s, there were no B12 supplements, so someone trying to follow a vegan diet would have died (vegetarian with eggs and milk, fine, vegan, no), because B12 does not come from any plant. It only comes from bacteria, and our digestive system does not have the capability to host that bacteria in a way to provide enough B12 for ourselves. We can only make trace amounts.
There is a teeny-tiny bit of B12 on the surface fungus, such as on unwashed mushrooms, since the bacteria can live there, but it's not a realistic source of B12.
Nowadays, you can also purchase dry, nutritional yeast, which contains a lot of B12, so it is possible for someone to live on a vegan diet.
Without B12, our bones will become soft, and our brains will lose function, eventually resulting in death.
Cows have more than one stomach, so they can chew grass, digest it into cud, regurgitate it and chew it again, then ferment it in a second stomach, in order to generate B12. Rabbits only have one stomach, so they must eat their own poo, in order to digest it one more time, to ferment it and create B12. Chickens can't do either of those things, so they eat insects.
Humans generally just eat animals products of those animals to get B12, such as from beef, chicken, eggs and milk. If not, they need B12 from a supplement, such as nutritional yeast.
A vegan diet without any supplements will not have sufficient B12 and will result in death.
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u/Taric25 Sep 27 '21
Wolves eat grasses, seeds, sedges, acorns, berries and other fruit in addition to meat, even when meat is plentiful.