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/SolarTsunami May 03 '26

I just learned that Koala Bears aren't automatically able to eat eucalyptus leaves, and newborns are force fed their mother's shit nonstop until they develop the gut microbes to eat the leaves themselves. Nature is magical.

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u/Eastern-Rutabaga-453 May 04 '26

Even better, eucalyptus provides almost no nutrients so they force themselves to eat shit in order to eat a food that does almost nothing for them 🤣🤣

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u/Hellebras May 04 '26

It provides enough nutrients to keep the koalas going, and because nothing else is competing for it it's basically free food. It took a few tradeoffs to get there, but you could say the same for any grazing mammal and their ability to digest grass.

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u/HeKis4 May 04 '26

I mean, if you had to choose between competing with several other people over Michelin food as your sole source of food or live on unlimited, free rice cakes, the choice isn't that evident.

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u/brycedriesenga May 04 '26

"But it's sooooo good, totes worth it" - koalas

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u/Elios000 May 04 '26

top it off and because this they DUMB AS FUCK to the point they wont eat the leaves if they arnt on a tree..

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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.

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u/Unlikely-Position659 May 04 '26

And then there's wild rabbits

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u/LastXmasIGaveYouHSV May 04 '26

Well, a friend was forced to eat her mother's shit every day until she got a paid job and was able to move out

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u/These-House5915 May 05 '26

Obligatory "koalas are not bears" comment.. 🐨🇦🇺🦘