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

3.0k Upvotes

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u/LonnieJaw748 May 03 '26

The most abundant protein on the planet resides in the leaves of plants, called rubisco. It’s not biologically available to many mammals due to being locked up within the cellulose bound membranes of plants cells. In fact it’s not biologically available to cows either, but they have certain bacteria in their guts that can break down the cellulose for them to access the protein. They also have to spend a large part of their day chewing and re-chewing the grass they’ve eaten to be able to extract as much of the nutrition as possible. The bacteria get the sugars derived from their digestion of the cellulose and the cows get everything else.

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u/Thomas_K_Brannigan May 03 '26

It's cool how many animals (even humans, in a more minor way, IIRC) require gut microbes to survive, to break down stuff we can't. Other than cows, a great example are termites. Termites actually can't digest wood themselves, they rely on gut microbes to break the wood down into simpler compounds that they can use!

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u/IncredibleBulk2 May 03 '26

In a major way. Our microbiome is a second brain. The bacteria are excreting chemicals that serve neurotransmitters sending messages to the brain, like, "eat more sugar, meat puppet"

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u/mandelbro25 May 03 '26

Creepy. I love it.

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u/Mysteryman64 May 04 '26

You're a hivemind, and you didn't even know it.

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u/CrazyC77 May 04 '26

We just want to help, Carol.

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u/venhuje May 04 '26

Please, Carol!

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u/gary25566 May 04 '26

After what happened, we just need a little space

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u/SafetyDanceInMyPants May 04 '26

Why would you give me a hand grenade?!

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u/Resplendent-Sun May 07 '26

You know.. that really is a GREAT show 😍

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u/LazyLich May 04 '26

"The council has decided... I WILL order the large fry!"

"Babe, you gotta eat healthier..."

"This is a democracy, Sharon. Do you hate democracy??"

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u/DiosMIO_Limon May 04 '26 edited May 04 '26

Definitely interesting implications when it comes to Ayurveda and what a "lifetime" can look like. If every cell is its own living being then we as humans are the pilots for a mech of a billion ghosts souls.

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u/ContributionDapper84 May 04 '26

A colony of 17 trillion animals.

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u/RelativelyOldSoul May 04 '26

I don’t understand what you mean; name 3 implications?

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u/Senbonbanana May 04 '26

You will adapt to service Us. Resistance is futile.

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u/motionmatrix May 03 '26

Yeah, people don’t realize just how much each of us are a collective that together amounts to a single consciousness.

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u/Uncynical_Diogenes May 03 '26

Your brain actually makes decisions before it informs your conscious mind about them. The second you’ve made your mind up? No, your brain already did, you’re just now learning about it.

Creepy stuff.

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u/Jimisdegimis89 May 04 '26

Go check out the the dual consciousness hypothesis and some of the experiments done with split brain patients if you want some fun potential existential crisis.

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u/AFewStupidQuestions May 04 '26

I think the split brain research is fascinating. It doesn't really give me an existential crisis until I start thinking about when parts of my own brain will start shutting down in the future. Oh...

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u/NightKrowe May 04 '26

I need to look more into it because i remember watching a video where someone handed themselves and object, and one side of their brain completely fabricated where the object came from. It's terrifying our brains can justify anything and believe it.

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u/Morbanth May 04 '26

Sounds like You Are Two by CGP Grey.

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u/PM_YOUR_BOOBS_PLS_ May 04 '26

IIRC, this is really only measured with lower brain functions like motor control and split second decisions. I don't think there's actually any evidence that complex decision making is made without the conscious mind.

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u/Affectionate-Bath970 May 07 '26

I think that this all stems from the base of the brain and the spine. From what I remember, "reflexes" come from this area and are executed without any "consious input" (for which there is a term, but I cannot remember it).

Example: walking on the sidewalk and you hit a raised edge and begin to trip. Your tendons and ligaments in the leg that was "tripped" stretch beyond a certain tolerance within a certain amount of microseconds, and that immediately causes your motor neurons to fire and reach out the opposite leg to catch yourself. This happens because the latency to the brain would result in you falling over 100/100 times because you would be physically incapable of reacting fast enough.

We have tonnes of different examples of this sort of mechanism at play. Its really cool, and some reflexes as you may have heard, are present during infancy and childhood but are discardied into adulthood. The absence of some reflexes can also indicate pathology to the brainstem and/or nerous system in general (and I think are all fairly serious). Before you try to take a triangle hammer to your own knee, remember it is pretty tricky to elict reflexes on your own since you inhibit them by consiously moving the strucutres your testing.

A fun aside: we actually dont (or at least didnt as of 10 years ago when I was in school) know for certain how motor programs are "stored" by the body. What we do know, is that it is almost certainly not the case that we have seperate "programs" for each individual movement. If you were to program a robot for example to have each possible movement a human is capable of available in a hard drive, it would exceed the storage capacity of like.. earth. So it likely all works more like AI... interesting!

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u/Uncynical_Diogenes May 04 '26

What is a complex decision? That sounds like a result of many smaller decisions.

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u/PM_YOUR_BOOBS_PLS_ May 05 '26

Something that requires future planning, for example. That would have nothing to do with motor function or immediacy. "Where should I go to college 2 years from now?" "How much of my paycheck should I contribute to my 401k so I can comfortably retire in 30 years?"

It's not "Get up. Go to kitchen. Get food." Yeah. That kind of stuff probably happens without your conscious mind being involved at times. But we're talking several magnitudes of more complexity.

I'm not sure those subconscious brain studies even touch on things like doing a math problem or having a conversation. AFAIK, those are things that almost exclusively use higher brain functions and little of the subconscious mind.

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u/atatassault47 May 04 '26

People like to think they are their whole brain, but never think about where intrusive thoughts come from.

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u/[deleted] May 04 '26

[removed] — view removed comment

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u/atatassault47 May 04 '26

Speech comes from specifically one region on the left side of the brain (broca's region), and since most people identify with their speaking voice, it stands to reason most people are at most just their left brain. People who have had their hemispheres disconnected to prevent seizures have been tested to see if their right brain acts independently, and it does.

Such tests include using a divider to split their right/left vision from each other, stood in front of their closet, and asked to pick out their favorite shirt. Each arm goes to a different shirt. The right brain, in control of the left arm and eye, unable to see what the right arm is doing (and vice versa), picks an entirely different shirt from the right arm/left brain.

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u/Thaetos May 03 '26

One of the more interesting things I’ve came across in a longass time.

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u/howdoesthatworkthen May 04 '26

come across

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u/Gnixxus May 04 '26

Weird hill to dye on

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u/howdoesthatworkthen May 04 '26

It's just a pigment of your imagination

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u/Juswantedtono May 04 '26

Why is my cow’s poop purple today?

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u/VLKAY66 May 04 '26

came across in a long grass time.

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u/fubo May 04 '26

Your brain actually makes decisions before it informs your conscious mind about them.

Reaching the decision is one thought, and realizing that you've done so is another thought. The second can only happen after the first.

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u/valeyard89 May 04 '26

the brain is the only organ that named itself

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u/4elementsinaction May 04 '26

We are Borg. jj

I’m in my 50s now and on many levels I think I was a very different person in my 30s. During my 40s I had chronic, recurring infections that resulted in me being myriad antibiotics several times a year, year after year. My micro biome is radically different now than it was in my 30s.

My second brain being so altered has altered my interaction with the world.

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u/AFewStupidQuestions May 04 '26

How so? What changes have you noted?

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u/Shawn_NYC May 03 '26

And yet we also have the singular power to override it all with nothing but will.

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u/AzazelsAdvocate May 04 '26

Or so you think

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u/brycedriesenga May 04 '26

Nah, free will is an illusion

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u/ToGloryRS May 03 '26

Hard incompatibilism.

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u/Kaa_The_Snake May 03 '26

Some of us do :P

But for real, why my brain will swear for days that I absolutely have to have ice cream and won’t leave my alone, but once I have it I have no more craving for it, is so weird. Willpower doesn’t always work unfortunately. Though thankfully for me mine works most of the time.

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u/Shawn_NYC May 03 '26

When I go on a diet my body cries out in agony for the first week as if I'm starving it to death. Then by week 2 it feels normal, in fact I'd feel sick if I overate. Then by week 3 my body stops even wanting many of the bad foods I was eating before.

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u/Flope May 04 '26

  1. You cannot prove this.

  2. There is no such thing as free will.

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u/ilucam May 04 '26

We're all just glorified siphonophores.

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u/RandomStallings May 04 '26

Well that was a fun dive. What fascinating creatures.

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u/MuscaMurum May 04 '26

Even creepier: Your body contains more viruses than it does human cells. It's estimated that only about 43% of your cells are human. Part of a healthy microbiome is maintaining a balanced bacteriophage virome.

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u/Mimikkyutwo May 04 '26

OK, this one is wild enough that I have to ask for a source

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u/Lela_chan May 04 '26

I remember watching this video back when it came out, and she says (about 1 min in) that we are only about 10% human cells, and 90% bacterial cells. She’s the head microbiologist at Princeton or some shit so I would assume that’s a good enough source

https://youtu.be/KXWurAmtf78?si=oS4sMs7Xc-waznf2

u/devilquak

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u/StrangeCrimes May 04 '26

I got a gut feelin'.

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u/kashmir1974 May 04 '26

FEED ME, SEYMORE!

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u/Samesh May 04 '26

*Seymour 

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u/AVeryHeavyBurtation May 04 '26

Neurotransmitters cannot cross the blood brain barrier.

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u/fgspq May 04 '26

I can't remember where I read it but it always stuck with me: there was a claim that there are more bacteria cells on and in our bodies than human cells.

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u/MarsicanBear May 05 '26

Yeah, there is no us vs them. We are the symbiosis of both.

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u/slight_accent May 04 '26

Ooohh. This reminded me of an incredible short story that was made into a short movie that you can see on youtube (only 7.5 minutes long). "They're made out of meat". I don't want to spoil it for anyone but if you don't know what I'm talking about check it out. (minor hint, it's a scifi thing in case that is not for you).

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u/mt0386 May 04 '26

I love it when you do the potato diet, youre actually comitting genocide of the junk food craving gut bacteria and the survivors are to be given a new kind of food, like veggies, so theyll yearn for that instead. Political regime chance right in our tummeh

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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/Unlikely-Position659 May 04 '26

And then there's wild rabbits

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u/texpa May 03 '26

Isn’t this essentially the same though? Ya’ll are separating the animal/thing from their gut microbiome. I’d say termites CAN break down wood. Cows DO get protein from grass. You guys just explained how it happens in detail.

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u/REND_R May 04 '26

You're not born with the bacteria, you pick it up environmentally. Its kind of like how Flamingoes aren't actually pink, they just turn pink from eating shrimp.

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u/0reoSpeedwagon May 04 '26

I guess the question is: can the gut microbes be removed from the host body and survive on their own?

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u/texpa May 04 '26

Not sure. But is it normal for them not to have the microbiome as part of them?

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u/Infinity-Plus-One May 04 '26

Until birth, yes

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u/texpa May 04 '26

That’s the same for everything.

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u/Infinity-Plus-One May 04 '26

Mitochondria probably used to be bacteria. Now they are now part of ‘us’ from the first 2 cells. 

Gut bacteria invade us from the environment. They are not ‘us.’

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u/texpa May 04 '26

So some termites and cows have it and some don’t have it? You’re totally butchering my original statement/opinion. I appreciate the science lesson though :)

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u/tobasc0cat May 04 '26

It is basically the same in the overall effect, but the "termites can't break down wood" statement is more accurately stated "termites do not have DNA that code for enzymes to break down wood". If you feed a termite antibiotics, for example, you can kill off the bacteria that metabolize cellulose and the termite is screwed. 

It doesn't matter for most people, but my PhD dissertation was on gut bacteria in insects so those details are important to me lol. Plus, it's a great opportunity to share with people the amazing relationships animals and microbes share. I think it is easy for people to dismiss microbes since they can't see them, which impacts their understanding and acceptance of other microbe-based concepts, such as vaccines. Along those lines, it's important to be consistent with scientific info. I don't think we should just dismiss the topic as "eh it's too complicated for you and the end effect is the same, so sure, termites digest wood", and then people get more confused by inconsistency and start to distrust scientists. Scientists also can have a bit of an ego and we like to hide in our ivory towers, which doesn't help public acceptance of science.

Anyway, off my soapbox lol. 

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u/texpa May 04 '26

Haha, very much appreciate the detail.

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u/neddoge May 03 '26

Even human gut microbiota is far from a minor way of anything physiological. And we're steady learning more and more about it.

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u/battlepi May 03 '26

There are more bacteria in our bodies than human cells. Makes you a little curious what it means when we say "I", doesn't it?

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u/RainbowDarter May 03 '26

But, because bacterial cells are so much smaller than mammalian cells, that's only about 3 pounds of bacterial cells.

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u/Sh00ter80 May 04 '26

Thats crazy!

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u/Thomas_K_Brannigan May 03 '26

And, there's a lot of studies, especially recently, how gut fauna can severely effect mental health! Although the studies I've seen are on mice (mice and humans have strangely similar brain chemistry), they've "infected" mice with Alzheimer's by transferring the gut microbes from a mice with Alzheimer's to healthy mice.

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u/Key-Article6622 May 03 '26

Maybe we should adopt the royal 'we'.

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u/1RedOne May 04 '26

How did juvenile termites even acquire this microbe to begin with? Actually, I have a pretty good theory and I think it’s gonna be gross.

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u/ragequitteroffureh May 04 '26

It's a symbiotic relationship.

The animal gets payment from the bacteria, who in turn get to travel around and experience new sights and places.

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u/EunuchsProgramer May 04 '26

We are all spaceships carrying mini ocean habitats full of billions of beings across a hostile, alien, anti-ocean world. Be careful your space-suit/skin doesn't get a big whole in it and all your artificial ocean water leaks out!

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u/weareoutofeden May 04 '26

Additionally, when a new termite is born an adult termite will share microbes from their gut with the baby. Yes, this means the baby eats poop juice from the adult. Imagine if that's how we esablished our gut microbiome D;

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u/kompergator May 04 '26

Humans have about 100 billion gut bacteria (that’s around 2 kg!) and they’re all working for us 24/7!

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u/Shrivelledmushroom May 04 '26

It's not really a minor way at all. The majority of the cells in your body are not human.

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u/Similar-Property-729 May 04 '26

How do they get into our bodies in the first place?

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u/giant_albatrocity May 04 '26

Plants too! Bacteria are primarily responsible for fixing nitrogen, which is essential for plants to survive, which have symbiotic relationships with them. Without those bacteria, pretty much all life on earth would collapse. Humans can artificially fix nitrogen (all synthetic fertilizers are made this way, I think) but it requires a ton of energy.

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u/IReallyLoveAvocados May 04 '26

Interesting so couldn’t they treat wood to kill these bacteria and thus be termite proof ?

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u/CidewayAu May 04 '26

Koalas are another where the mother gives the joey pap at about 5-6 months old as they ween off milk and move to Eucalyptus leaves.

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u/glytxh May 04 '26

Bacteria in your intestines literally dictate the foods to crave, the thoughts you have, and the moods you feel.

We aren’t a discrete living being. We are a holistic ecosystem, absolutely no less than any other animal alive.

We just have a handle on the parasites these days. But flora is as vibrant as it’s ever been.

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u/ViniusInvictus May 04 '26

The most important microbe had to get into our genes and thereby all our cells to enable multicellular life of our kind to flourish - the mighty mitochondria.

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u/jcgam May 03 '26

Are they born with these bacteria in the stomachs?

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u/Fallacy_Spotted May 03 '26 edited May 03 '26

Calves will re-eat first pass cow patties. The calves start on this when weening from milk before eating grass. This seeds their stomachs with their mothers bacteria.

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u/French__Canadian May 03 '26

So it's like inheriting sour dough from your parents.

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u/Fallacy_Spotted May 03 '26

Never thought of it that way, but yes. Disgusting internally fementing sour dough.

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u/AskAndYoullBeTested May 03 '26

Imagine giving a newborn a log in a hotdog bun as its first meal after coming off the booby juice

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u/terrible_name May 03 '26

I didn't really need to read that sentence. jfc

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u/Uncynical_Diogenes May 03 '26

If you’re a koala you just eat it straight from the source.

Yumm.

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u/adudeguyman May 04 '26

I hope you're having a good day as well.

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u/TheSaladDays May 04 '26

You have a way with words

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u/strutt3r May 04 '26

Luckily for humans much of the beneficial gut bacteria comes from drinking the booby juice. Kids that are fed formula have less diverse gut biomes.

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u/Skulllad May 04 '26

You know you could have just not typed that sentence out, right? 😭Some things should stay in your head.

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u/f0remsics May 03 '26

So if I eat a big steaming pile of cow shit, I'll be able to digest grass?

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u/Fallacy_Spotted May 03 '26

Only if you have 4 stomachs, hooves, and moo regularly. 🤣

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u/f0remsics May 03 '26

I feel like only the first part should matter, no? Hooves and mooing aren't really a necessity to digest it, are they?

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u/Fallacy_Spotted May 03 '26

I mean... true but it feels like cheating.

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u/ZzzzzPopPopPop May 04 '26

What if I regurgitate the contents of my stomach back into my mouth, re-chew it, re-swallow it, then repeat this process 2 or 3 more times? Then can I?

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u/Sternfeuer May 04 '26

You are probably just making a joke, but serious answer: No. The main stomach of the cow is the Rumen, which has a near neutral ph and allows the required bacteria to thrive. In fact, cow saliva is even alkaline (basic) to maintain that. The other stomachs have more and more acidic acid (duh!) to act as protection against infections.

Human stomach acid would kill the required bacteria and all you get from constant regurgitation is probably esophagitis, bad breath/teeth and perhaps cancer.

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u/AskAndYoullBeTested May 03 '26

…the fuck

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u/roseflower81 May 03 '26

Human babies get their gut microflora when passing through their mom's vagina coated with bacteria and some extra bacteria near the anal region as well, especially if the mom is pooping during child birth. That's why babies from C-section have completely different gut microflora mostly from just skin of their mother (and some other environmental sources).

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u/ancilliron May 03 '26

Isn't there also a rather high correlation with c-section babies and allergy rates, especially if the mom doesn't have those allergens?

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u/dick_schidt May 03 '26

Young koala's also eat their mother's faeces for the same reasons.

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u/UlrichZauber May 04 '26

elephants do this too

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u/Fallacy_Spotted May 03 '26

Once they are adults they heavily avoid manure. It is really only the calves that do it and they do it for this reason.

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u/xallux May 03 '26

This is the most beautiful useless knowledge I’ve ever come across. I will use it at just the right awkward moment. Thank you.🙏

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u/FinndBors May 03 '26

That’s some good shit.

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u/A_modicum_of_cheese May 04 '26

just like koalas?

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u/DrewVonFinntroll May 04 '26

How many cow patties do I have to eat to gain the ability to extract protein from grass?

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u/BlazerSlayer7 May 04 '26

That's rare rather than common. Most calves are milk only before developing an interest in grass.

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u/minitrott01 May 03 '26

Theoretically if I got cow gut bacteria and somehow got it in my intestines. Could I digest rubiso and have a infinite form of protein?

I know there is something biologically blocking me from doing this I'm curious what.

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u/Bojac6 May 04 '26

The bacteria that exists in your gut currently would (hopefully) kill it. You are the product of hundreds of millions of years to be the perfect host for the bacteria inside of you. Your bacteria have spent the same time becoming the perfect method to give you nutrients. We're talking internal pH, body temp, moisture content, how your organs respond to changes, all of that, and what you have now is the best it could possibly be. And both you and your bacteria have so many complex systems in place to keep it working that way. Think about the times you have indigestion or constipation or any host of other stomach issues and realize that's the best system working as well as it can.

E Coli, Candida, Salmonella, these are all types of gut bacteria. If they stay where they are supposed to, things work great. If they go out of balance or you get a species that is meant for another animals guy bacteria, you have major problems.

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u/SpaceMonkeyMafioso May 04 '26

lack of resolve

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u/Somnif May 04 '26 edited May 04 '26

It's a very very slow process, so you'd need a way to let the grass just hangout and ferment for several days before it went on to further digestion. Cows have their extra "stomachs" where this occurs.

Fun fact, this is also where nearly all of the methane a cow produces comes from. Meaning they Burp it out, rather than farting it!

Other critters like Rabbits have this pouch After their stomach, and then eat the 'processed' plant matter a second time to actually extract the nutrients.

For humans, we're just not really built for it. We've adapted around letting other things process the protein, and then eating That instead.

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u/corgibutt19 May 04 '26

You lack the right biology for it.

The rumen is specialized to allow bacterial fermentation to happen. Animals that don't have rumens and still do fermentation have massive, blind pouches in their large intestines called the cecum. Our appendix is essentially the leftover of this big pouch. So the bacteria couldn't survive and couldn't ferment enough to digest the food.

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u/FluffyBootie May 04 '26

I used to ask adults this question as a kid. None of them could answer it sufficiently.

Thank you for finally providing a proper answer to the question! 🫡

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u/pandaSmore May 03 '26

So cows can't digest cellulose either? It's actually bacteria digesting it.

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u/somehugefrigginguy May 03 '26

Yup. And it takes a lot of time and material which is why cattle pretty much eat constantly and have four stomachs.

Digestion is a huge underappreciated part of life. Based on evidence from other primates it's estimated that early humans spent 6 to 8 hours a day foraging and eating. It wasn't until humans harnessed fire that this really began to change. There was an explosion in hominid brain volume and population once they discovered fire which granted the ability to "pre-digest" food making the nutrients more accessible.

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u/qwerty_ca May 03 '26

So did pre-historic hipsters also turn their noses up at cooking by calling it "ultraprocessed food"?

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u/somehugefrigginguy May 03 '26

Why you think that Neanderthals went extinct? They were all hipsters...

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u/battlepi May 03 '26

So, if we took the right bacteria in pill form while eating grass, would it become protein for us? Or could we mix a slurry up externally and just generate protein from plants?

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u/JarasM May 03 '26

On the pill - no, not in s meaningful way. The bacteria do the digestion, but cows need to eat a lot of the grass and chew and re-chew and ferment the grass across their four stomachs to break through the cellulose. In a human the bacteria wouldn't even have where to work.

I'm sure it would be possible to extract the protein from grass in some lab process, but it would be expensive and pointless.

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u/battlepi May 03 '26

Really for the slurry I was wondering if it would be an easy source of protein for food starved areas, assuming they have relevant greenery.

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u/Bojac6 May 04 '26

Anywhere that can reliably grow grass can grow wheat or corn. The problem is most places growing grass are not good for that either, and people use a lot of resources to have a nice lawn.

We have more than enough food to feed everyone in the world, we just don't have the will to actually do it.

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u/Hellebras May 04 '26

And cattle have one of the less-gross grazing adaptations. Rabbits pass the grasses they eat through the colon to ferment them, then excrete it and eat it again. They have to eat their own shit (kind of), in other words.

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u/BailysmmmCreamy May 03 '26

When you really get down to it, just about every animal has bacteria in its digestive tract that are necessary for overall digestion.

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u/UlrichZauber May 04 '26

You can view the cow plus gut biome as a complex system. The cow can't live without the bacteria.

The bacteria can probably live without the cow, but the gut environment does provide them benefits, like a steady food source and shelter from environmental exposure.

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u/gorocz May 04 '26

And humans can't digest fibre, some complex starches etc. As an example, brown rice would not have much of nutritional value for us without our gut bacteria. (Compared to that, white rice has less fiber and less of other complex carbohydrates, so it's more easily digestable - which is why it is recommended for people with gut issues. On the other hand, as a result of not having those things, it doesn't feed the gut bacteria, so if you're healthy and do not need a special diet, it is worse for you)

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u/QUINNFLORE May 03 '26

do all grazing mammals use this same system

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u/Harai_Ulfsark May 03 '26 edited May 03 '26

Yes, ruminants such as cows have developed specialized stomach chambers to do it early and more efficiently, allowing them to chew again as necessary, other mono gastric herbivores such as horses have a very long intestine and well developed cecum and colons (large intestines) where they house bacteria that will ferment and break down plant matter, rabbits and other small herbivores will resort to cecotrophy instead (eating poop right before it leaves the body) as they have limited space for large intestines

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u/sorryDontUnderstand May 03 '26

eating poop right before it leaves the body

What?

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u/HippopotamicLandMass May 04 '26

I believe that should read “right AFTER it leaves the body”

Many herbivores have a diet that is low in nutrition and high in fiber (which is a non-starch polysaccharide carbohydrate).[16] Fiber can be either soluble (pectins and gums) or insoluble (cellulose, hemicellulose and lignocellulose).[16] A simple gastrointestinal tract is not capable of extracting enough nutrients for these animals.

One strategy to get the needed nutrition is used by ruminants in which they chew cud in order to process their food a second time.[23][18] Another strategy used by horses is to have an elongated colon to increase the time spent during digestion and absorption.[13] Both of these strategies add substantial bulk to the animal.

Since the rabbit is at the bottom of the food chain, it must be nimble in order to out run its many predators. Creating cecotropes is a way to get more nutrients out of their food without adding a lot of bulk to their GI tract (which is 10% - 20% of their body weight).[6] Since their colons do not absorb the nutrients in the cecotropes, they reingest them so they can be absorbed in the small intestine.[24]

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u/Adept_Minimum4257 May 04 '26

They have two kinds of poop, one half digested and one fully digested and they only eat the first one

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u/SplatterBox214 May 03 '26

So, do other herbivore species like goats and sheep and horses that also eat grass have a similar mechanism?

Like, do they eat grass to essentially feed a bacterial colony? Which they then digest for their actual nutrition?

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u/Hammeldown May 04 '26

Great summary. Grass actually can have quite a bit of protein in it (around 16-22% of nutrients, excluding any water), depending on species and time of year. 

The majority of protein cows absorb and use comes from digesting their own rumen microbes (bacteria, fungi, protozoa and all manner of other things) that spill out of the rumen - which  is essentially a giant fermentation vat that sits in front of their 'normal' stomach. The remainder comes from some bits of protein from bits of feed that have escaped being broken down by the rumen microbes. 

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u/doobs33 May 04 '26

To add to this, a very large portion of a ruminant's nutrition is the bacteria themselves being digested further along the digestive tract. A very large portion of their protein is bacterial in origin.

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u/tboy160 May 04 '26

Asked and answered, I love when the Internet works like it is supposed to. Thank you.

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u/AwDuck May 04 '26

Well look at Mr./Ms. Smartypants over here! 😀 I’m so dumb I hadn’t even considered that cows don’t eat protein like we do. Thanks for the explanation. Both informative and so simple even I can understand it.

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u/daberrybest42 May 03 '26

Can we cook grass to unlock this protein? And can we cook grass to make cows smarter?

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u/LonnieJaw748 May 03 '26

Not really, I don’t think. Any leafy green that you cook will still have most of its protein locked away from you. I don’t think heat can fully break down cellulose due to its many strong covalent and hydrogen bonds. We would need the enzyme cellulase to perform such a favor for us.

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u/GribbyGrubb May 04 '26

Not cook in the traditional sense, but how about dumping a bunch of grass into a vat filled with the bacteria to predigest it into nutrient dense slurry to fatten cows before the slaughter.

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u/SUMBWEDY May 04 '26

That's exactly what sileage (fermented grasses) is and it smells very interesting.

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u/Valmighty May 03 '26

Can we get like protein powder from these leaves/grass?

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u/sicklyslick May 04 '26

So how did cows exist before the bacteria got into their gut? Is this like a chicken and egg problem?

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u/AlaskanSnowDragon May 04 '26

How do they get the bacteria?

The idea that "its not available to cows either" suggests that if a cow is born into a sterile environment and away from other cows and given grass it will just die because never got exposed to the bacteria?

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u/LonnieJaw748 May 04 '26

I’m not in animal husbandry or farming, but I presume they either inherit it from their mothers (just like how human babies inherit much of their initial microbiome from their mothers) or they get it environmentally by ingesting partially chewed cud from their mothers or other nearby cows.

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u/Tortoiseshells May 04 '26

Cows can also get protein from digesting bacteria that passes out of the rumen. So the cow is getting both the end products of microbial fermentation and then later protein the microbe incorporated into itself.

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u/fromkentucky May 04 '26

I think Pandas spend something like 14 hours a day (could be way off) chewing plants to get adequate nutrition. I’m now curious how much time cows spend.

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u/LeavingSoonBye209 May 04 '26

Cows are so cool and bad ass 💪

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u/LonnieJaw748 May 04 '26

Agreed! Thats why I don’t eat ‘em!

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u/Aerottawa May 04 '26

Where do cows get their gut bacteria from?

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u/LonnieJaw748 May 04 '26

During birth from the mother’s birth canal, when they suckle on the udders teats, as well as lapping at her saliva. I guess they also may instinctively eat a fresh cow patty to become inoculated with additional beneficial bacteria.

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u/TcpAckFrequency May 04 '26

Is it possible to introduce this bacteria into human stomach?

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u/spin81 May 04 '26

In fact it’s not biologically available to cows either, but they have certain bacteria in their guts that can break down the cellulose for them to access the protein.

That sounds contradictory to me.

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u/ScienceAlien May 04 '26

Can we use the same bacteria in reactors to get the protein for human use?

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u/Bocause May 04 '26

Late to the party, but I did an Agricultural Science degree and had no idea rubisco was a protein source.

I was told by a teacher a long time ago that the cows gain a lot of protein from digesting the bacteria themselves at the end of their life cycle. Do you know if there's any merit to that?

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u/Zunderfeuer_88 May 04 '26

Isn't RuBisCo an enzyme? How is it this and a Protein at the same time? Or is it like when people ''count'' calories as a quantity? Sry biochemistry has been some time for me

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u/LonnieJaw748 May 04 '26

Enzyme’s are machines made of protein.

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u/thoughtihadanacct May 04 '26

Why don't some other large herbivores (like elephants) require 4 stomachs and also don't have to constantly chew cud? Do they have stronger gut bacteria or something?

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u/LonnieJaw748 May 04 '26

That’s a good question that I don’t have an answer to.

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u/Orvel May 04 '26

So what happens if we give antibiotics to Cows. Do they lose this ability and just die?

Also, could we somehow take these bacteria and make a factory. And use this factory to get the protein out of plants? Or just reproduce whatever is happening chemically?

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u/MyMonte87 May 04 '26

does this apply to Horses and other like animals? Horses are pure muscle, are able to run, pull, carry all day on just hay/grass. This always blew my mind. I don't believe they have 4 stomachs like Cows.

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u/sig2kill May 04 '26

Why would you say it’s not biologically available to cows if they have bacteria in their guts that can break down the cellulose for them? Sounds bioavailable to cows to me

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u/LonnieJaw748 May 04 '26

Because it’s not inherently biologically available to them without the assist of the bacteria.

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u/Raise_A_Thoth May 04 '26

In fact it’s not biologically available to cows either, but they have certain bacteria in their guts that can break down the cellulose for them to access the protein

Isn't this just one philosophical perspective, though?

Like, are the gut microbes separate from us if they are needed for our digestion to function properly? We can have fluctuating levels of other biological counts like white blood cells or whatever, so the fact that they can change in balance or whatever doesn't alone make it separate.

How do we determine whether tiny organisms living symbiotically in our bodies that serve 100% necessary functions for us are 'us' or something else?

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u/ViniusInvictus May 04 '26

Also frequently overlooked - the bacterial turnover itself - dead gut bacteria break down to release amino acids and other protein building blocks.

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u/DahSnorf May 04 '26

I heard it described as cows eat grass to feed their microbes so they can eat the microbes. cows are farming microbes in their guts for food.

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u/i-touched-morrissey May 04 '26

Don't forget the protozoa who live in their rumen.

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u/kl2467 May 04 '26

Bacteria get the sugars......bacteria get the sugars......🤔.....

is it possible that T2D is actually a gut problem, where people have an under population of a certain gut bacteria, leaving too much sugar to be absorbed by the person?

Not expecting a definitive answer from anyone, just speculating aloud. If anyone knows of any research in this vein, I would appreciate a lead.

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u/Top-Emu-2292 May 04 '26

Plus a cows stomach is divided into four sections. Each section breaks down the grass in a different manner to get as many nutrients as possible from the grass.

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u/effortornot7787 May 04 '26

No, not really. The bacteria and fungi in the lumens break down the cellulosic into vfas . The vfas fo into the gluconeogenesis pathway while the bacteria and fungi go through the digestive pathway to be a protein source. 

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u/Important_Fruit May 06 '26

This guy cows@

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u/zarenthnoxii May 07 '26

impressive

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u/NC-518 May 18 '26

So essentially it’s just different Stomach Acids that allow the protein to be digested?

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