The Factory Inside the Cow

The Raw Material

Start with how much she eats.

A cow eats, every day, somewhere around two percent of her own body weight in dry matter — the part of the feed that is left once the water is taken out. On poor forage it is a little less. On good green pasture, or when she is nursing a calf, it can run to two and a half or three percent.

She does not eat it in meals. She harvests it. Up to eight hours a day, head down, taking somewhere between 25,000 and 40,000 bites before sundown.

Every one of those bites is being fed into a machine. But first she has to get the grass off the ground, and she does not do it the way you would guess.

The Bite

Look in a cow’s mouth and the first surprise is what is missing. She has no top front teeth.

Where your upper incisors are, she has a hard, rubbery plate called the dental pad. Her front teeth are all on the bottom.

So she cannot nip grass the way a horse does. Instead, her tongue does the work. It sweeps out in an arc, wraps around a bunch of grass like a hand, and pulls it back across the lower teeth and against the pad. The grass is not so much cut as torn.

That has consequences you can see from the fence line. Because she grazes with her tongue, a cow struggles to get closer than about two inches to the soil, and she grazes best when the grass stands around six inches tall. A sheep, with its split lip, can take a pasture much lower. A horse, with teeth top and bottom, can graze nearly to the dirt.

The cow is built to take the top of the grass and leave the plant alive to grow back.

And she barely chews it on the way down. She is not eating yet. She is loading.

The Vat

What she swallows goes into the rumen, the first and largest of her four stomach compartments — and the reason this whole story exists.

The rumen is enormous. In a mature cow it holds 25 to 40 gallons. Together with the compartment next to it, it makes up 84 percent of her stomach, and her stomach as a whole fills nearly three-quarters of her belly. When you look at a cow from behind and see that great round barrel on her left side, you are looking at it.

It is not really a stomach in the way yours is. It makes no acid and no digestive enzymes of its own. It is a fermentation vat: warm, wet, airless, and alive.

The vat never stops moving. Once or twice a minute its walls contract and roll the whole mass over, mixing fresh grass into the older, half-digested material and the soup beneath it.

And it is constantly being topped up with saliva. A cow makes 50 to 80 quarts of it a day, and more when she is chewing hard. That saliva is loaded with bicarbonate — baking soda, in effect — and it is what keeps the vat from turning sour. Left alone, fermentation makes acid. The cow neutralises it with her own spit, and holds the rumen close to neutral, around pH 6.2 to 6.8.

She is running a brewery in her belly, and managing the chemistry with her mouth.

Chewing the Cud

Here is where it gets strange.

Grass that has soaked in the rumen for a while comes back up.

A contraction of the compartment beside the rumen pushes a soft ball of fermented grass — the cud — into her throat, and it travels back up to her mouth in a wave that runs the wrong way. She chews it, slowly and completely, thirty to sixty times over about forty seconds. Then she swallows it and brings up the next one.

A cow’s day, in other words, splits roughly into thirds: grazing, chewing her cud, and resting.

Why do it twice? Because fiber is tough, and microbes can only attack a surface. Every chew breaks the grass into smaller pieces with more surface for them to work on. Rumination also pumps saliva into the vat, which keeps the chemistry steady.

The next time you see cattle lying in a pasture in the afternoon, jaws going side to side, they are not idle. They are working.

Dry Grass Into Food

This is the part nothing else does quite this way.

Much of a blade of grass is fiber — cellulose and its close relatives, the stiff material that holds a plant upright. Cellulose is made of sugar. It is also locked so tightly that no mammal can open it. Not people, not dogs, not pigs, and not cows. No mammal’s body is known to make the enzyme that breaks it.

The microbes make it.

Inside the rumen, specialist bacteria and fungi latch onto the chewed grass and dismantle its fiber piece by piece. They ferment the sugars they free, and they leave behind simple fuels called volatile fatty acids — mostly acetate, with some propionate and butyrate. The cow absorbs those straight through the rumen wall.

That is the difference between an animal that lives on grass and one that can only garnish a plate with it.

And energy is only half of it. The other half is protein.

The microbes eat, grow and multiply by the billion. They are, themselves, largely protein. As the rumen empties, they wash downstream with everything else, and the cow digests them. The bugs become her food. Depending on the diet, these microbes supply half or more of the protein her body actually absorbs, and on some diets nearly all of it. Along the way they also make vitamin K and every one of the B vitamins she needs.

She does not really live on grass. She farms microbes that live on grass, and then she eats the microbes.

Now go back to that handful of dead winter grass. It might be four percent protein, well below what a cow needs. And she still gets by, because of one more piece of engineering.

Every animal breaks down protein and makes a waste product called urea. You get rid of yours. A cow on poor forage sends it back. Researchers feeding cattle low-protein prairie hay found that more than 95 percent of the urea her body made was recycled into her gut instead of being thrown away, some of it by way of her saliva. There the microbes turn it back into protein. On that hay, recycled urea supplied about a third of the nitrogen in the microbes’ own protein.

She even picks her food. On dormant range where the grass averages four percent protein, a cow will select a diet closer to six, pulling the best leaves out of the worst pasture.

Waste in. Protein out. From grass that has already died on its stem.

The Rest of the Line

The rumen is the heart of the factory, but it is only the first stage.

The reticulum. Right next to the rumen, lined with a honeycomb pattern, it works as a sorting bay. Heavy things sink into it, which is why it is also where a swallowed nail or piece of wire ends up. Ranchers have long fed cattle a small magnet that sits there for life, collecting metal before it can do harm. Its contractions are what send the cud back up.

The omasum. A compartment packed with folds of tissue stacked like the pages of a book, which is exactly what old stockmen called it. Its job is to squeeze water out of the flow and absorb it, along with more of the fermentation fuels.

The abomasum. The true stomach, the one most like yours. It is the only one of the four with glands. It pours in acid, dropping the pH to around 3.5 to 4, and enzymes that begin digesting the protein — including those billions of microbes.

The intestines. Then comes the small intestine, a tube up to 150 feet long, about twenty times the length of the cow herself. This is where the protein, the fats and what is left of the energy are finally absorbed into her blood. Past it sits a smaller back-end chamber, the cecum, about three feet long, where a second, lesser round of fermentation squeezes out what the rumen missed.

How long does it all take? For hay, the fiber may spend about thirty hours in the rumen alone, and two days or more travelling the whole length of the animal.

What Comes Out

At the end of the line is manure, and there is a lot of it.

On a pasture, that is not waste. It is the return trip. What the cow took from the grass she hands back to the soil, ready to grow the next bite.

She also breathes out and belches the gas the fermentation makes — somewhere around 130 to 260 gallons a day, roughly two-thirds carbon dioxide and a quarter methane. It is the exhaust of the factory, and a cow that cannot belch it is a cow in serious trouble.

Grass Into Muscle

Now put the whole factory to work on a calf.

A calf is not born a ruminant. At birth its rumen is small and asleep, and a fold in its throat sends milk straight past it to the true stomach. Only as it starts nibbling grass does the vat wake up, filling with microbes over the first two or three months of life.

Once it does, the numbers are remarkable. A weaned calf of 500 or 600 pounds, put out on good grass, can gain a pound and a half to two and a half pounds a day. On grass alone, a steer finishes somewhere around 1,000 to 1,200 pounds.

Six hundred pounds of animal, built out of sunlight, water and a plant no person can digest.

Scale that up and the economics come into focus. A study of the whole United States beef chain found that across a beef animal’s life, about 82 percent of everything it eats is forage, and only 10 to 15 percent of its feed is anything a person could have eaten instead.

Another study counted the protein. At the start of the chain, on the ranch where the cows live on grass, the herd produced something like 2,600 times more human-edible protein than it consumed. The numbers narrow sharply once cattle move into feedyards and eat grain. Across the whole chain, pound for pound, it comes out roughly even. Once you account for the higher quality of beef protein, it comes out ahead.

And about 29 percent of all the land in the United States is grassland pasture and range. Much of it is too dry, too steep or too rocky to plough. For people, it grows nothing to eat. For a cow, it is dinner.

The Ledger

Here is the whole story in one line.

A cow is a walking factory that takes the toughest, driest, least edible plant on the land and turns it into energy, protein and muscle.

She pulls the grass up with her tongue. She floods it with her own baking soda. She ferments it in a forty-gallon vat stocked with more microbes than there are stars in the galaxy. She brings it back up and chews it for a third of her life. She recycles her own waste into protein. She eats the microbes that ate the grass. And she hands the leftovers back to the ground as fertiliser.

Sheep, goats, deer and bison share the same basic design. But no other animal runs it at the scale cattle do, across the land cattle use, building muscle the way a steer builds it.

The next time you drive past a pasture and see cattle lying down, jaws working, looking like they are doing nothing at all, remember what is actually going on in there.

They are running the oldest food factory on the ranch. And it never shuts down.