How is there so much protein in cow’s milk when a cow’s diet consists mostly of grass which I assume is mostly fiber?



There’s a significant amount of protein in milk and I’ve always wondered how this is possible considering cow’s just eat grass? Does their stomachs convert grass into protein in a special complex way or something? I don’t understand?

In: Biology

The carbs in grass get rebuilt as the plant matter is digested through the cow’s intestines. They become amino acids and then are built again as protein and other stuff for the cow’s milk and so on.

Cow stomachs contain a lot of bacteria that can digest the grass and produce energy/protein for their own use. The bacteria, in turn, are digested by the cow, which then breaks down those proteins into amino acids and uses those to build their own proteins.

When you say “so much”, what do you mean? There’s only about 3.4g of protein per 100g of milk; compared with pretty much all other animal products that’s not that much.

That aside, grass also has protein, fats and sugars; all living things do. Cow digestive system is also very efficient and bacterial fermentation helps extract nutrients from within cell walls, which gives them enough amino acids to constitute proteins for muscle, milk etc.

All animals are able to synthesize the amino acids that make up protein, even humans. Not all are able to produce enough of all the amino acids they need though. But especially herbivores needs to produce a lot of amino acids that they do not get thorugh their diet.

In answer to your bigger question: there’s a shitload of proteins that the body uses, and it can make *most* of them from simple carbs – it’s like lego, but we do it with molecules.

However, there’s a handful of proteins that we can’t create from scratch, so we need to eat those specific ones in order to have a full set. We can get those from other animals, or certain vegetable sources. Most vegetable sources aren’t the complete set, but get one or two different ones going and you’re good.

Cows (and a lot of herbivores) can make most (all?) proteins from scratch themselves, so they don’t have to worry; they can get everything they need from grass.

The tricky part with a vegan diet for humans is getting the calcium, protein and iron content we need. It can be done, but it takes a bit of planning, especially if you don’t want to be eating 5000 calories of pulses or 20kg of leaves a day.

Herbivores need to eat protein to build their muscles etc. just as much as carnivores do. Plants are able to create proteins out of base elements, but all animals need to consume other living things to get most of the blocks to build their own proteins. Grass just has much *less* protein per unit weight than meat has, which is why a carnivore eats pretty rarely and a cow spends pretty much every waking minute eating grass.

Cows actively prefer high-protein grasses! Must taste better to them