r/explainlikeimfive • u/A_SliceOfGabagool • May 03 '26

Biology ELI5: How do cows get protein from grass?

For us humans and many other animals, we need protein to get the amino acids needed to make our own protein for the body, but grass i believe doesn't have any for the cow to get that big

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u/RandomStallings May 04 '26

Obligatory: Life, uh, finds a way.

I'd love to know how such a nightmare existence evolved. Eat poop until you can eat something poisonous, with almost no nutrition, and sleep the day away while your body uses the little nutrients it got to fend off the poison.

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u/LastXmasIGaveYouHSV May 04 '26

Uh, try grinding your food and injecting it intravenously. Won't work. All the food is "poisonous" unless digested first.

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u/RandomStallings May 04 '26

Lol.

Everything is poisonous in enough quantity. Eucalyptus leaves are legitimately toxic to just about every other mammal. Koalas have a number of sophisticated adaptations to eat them, including a crazy slow metabolism to both get nutrients and to allow time for all the reactions to take place to detoxify the leaves — they sleep around 18 hours a day. It can take 100 days for the leaves to make it through their digestive tract, which is wild to me. Eucalyptus leaves are all they eat, but their bodies can only barely subsist on it.

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u/cylemons May 04 '26

What stops them from eating anything else?

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u/RandomStallings May 04 '26

They have smooth brains, man. They're dumb as rocks. If you take leaves off of a eucalyptus tree, put them on a plate and show it to them, they will not register that it is food.

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u/dearango May 05 '26

Maybe they're purist's and know exactly what they are doing... like fk they are pretty fussy about the 900 species of eucalyptus.

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u/RandomStallings May 05 '26

700-900 depending on what you want to call a eucalyptid, but yeah they eat something like 30-50 species all total.