Ruminants: How A Wet British Hillside Becomes Dinner

71% of the farmland in the UK is growing grass, and there isn’t a human being alive who can make a meal of it.

The juice bar will press a fistful into a shot glass and charge you for the privilege. That is as far as our species has ever got.

On the Berwyn, above the Ceiriog valley, the ground is heather, rushes and acid peat. The rain comes in off the Atlantic at an angle, and any plough dragged up there would give out long before the slope did. A Welsh Mountain ewe stands in the middle of it, heavy in lamb, eating steadily and entirely unbothered. By May she’ll have turned that hillside into a lamb, and by the summer shearing into a fleece. The milk she makes from it goes to the lamb, since nobody on that mountain has ever volunteered to milk her.

The animal that can do this is a ruminant, and it is the reason most of Britain’s farmland feeds anybody at all.

Nearly half of that farmland is officially designated Less Favoured Area, which is the civil service’s way of saying the soil, the slope or the weather has ruled out most of the alternatives. In Wales the figure is 80%. In Scotland it is 85%. If that ground is going to feed anyone, it will be through a ruminant, and these islands have been making that call for 6,000 years.

A ruminant is an animal that has contracted its digestion out to microbes and grown a stomach big enough to house them. Cattle, sheep and goats are the ones that matter on British ground, with red deer on the hills beside them, and each has a long story of its own on this site: the goat, the sheep and the cow, with the whole herd gathered in the livestock series.

A field of grass is a larder with the door welded shut

A blade of grass is built largely out of cellulose, the most abundant organic compound on the planet. Cellulose is glucose, the same sugar your blood runs on, chained together by a bond that no mammal on Earth makes an enzyme to break.

The cow can’t break it either. She keeps lodgers who can.

We gave up on the whole business a long time ago. Over the last 2 million years the human gut shrank while the human brain swelled, and the part that shrank most was the fermenting end. In a chimpanzee, more than half the gut by volume is colon, a long slow tank where plant matter is rotted down into something usable. In a human it is about a fifth. We swapped the vat for the brain, then went looking for animals that had kept theirs, and how that swap happened is a story of its own.

A cow has one stomach, and most of it is a brewery

Ask any pub quiz how many stomachs a cow has and it will tell you four. Open one up and you find a single stomach split into four compartments, each with its own trade. The quiz has been giving the wrong answer for decades and has never once lost a round over it.

The first and largest chamber is the rumen. In a grown cow it holds well over 100 litres: warm, airless, never empty, and packed with bacteria, protozoa, fungi and archaea that between them do everything the cow cannot.

The second, the reticulum, is lined with a honeycomb pattern and catches whatever is heavy. That includes the fencing wire and stray nails a grazing cow swallows without noticing, which is why a cow can be given a magnet about the length of a finger to swallow on purpose. It sits in the reticulum for the rest of her life, quietly collecting ironmongery.

The third, the omasum, is stacked with folds of tissue like the leaves of a closed book, which is why butchers call it the bible and country people called it the manyplies. It wrings out the water.

The fourth, the abomasum, is the one that works like yours, with acid and enzymes and digestion you would recognise.

Everything goes into the rumen first, and a good deal of it comes back up. That is the cud. A cow lying in a field apparently doing nothing is re-chewing her breakfast, grinding the fibre smaller for the microbes and washing it down with saliva laced with bicarbonate, which stops the vat going sour. The whole family is named after the habit: ruminant comes from the Latin for chewing over.

What the microbes make of the grass, as far as the cow is concerned, is fat. They ferment it into short-chain fatty acids, acetic, propionic and butyric, which soak straight through the rumen wall into her blood and supply up to 70% of her energy. Britain’s most famous plant-eater spends its days running largely on fat.

The fermentation gives off gas as well, methane among it, which leaves the front end of the cow in a steady run of belches and has been the subject of more government reports than any other burp in history.

The cow farms bacteria and eats the harvest

The lodgers don’t get to stay. They multiply so fast that the rumen is constantly spilling them onward, and the surplus washes down into the abomasum, where the acid kills them and the cow digests them like any other meal. Between 50% and 90% of the protein reaching a cow’s small intestine is microbial. A dairy cow can live, and milk, on microbial protein alone.

So the grass is the fuel and the raw material, and the muscle on the animal has been assembled largely from bacteria she grew and then ate. The brisket on your board was built, at one remove, by a very well-run farm of microbes.

The same lodgers make vitamin B12, which no plant and no animal can make for itself, you included. They need cobalt to build it, and on cobalt-poor ground the lambs show it: they go off their food and waste away standing in perfectly good grass, fleeces open and ragged. Shepherds in north-west Scotland called it pine. The cure is a little cobalt, given to the microbes.

The B12 in a lamb chop was manufactured on site.

The rumen saturates the fat before it reaches the meat

Grass carries very little fat, and what it does carry is mostly polyunsaturated, the fragile kind with its double bonds exposed.

The rumen’s bacteria can’t stand it. Researchers in Aberdeen exposed 26 of the rumen’s commonest bacterial species to linoleic acid, the fatty acid most seed oils are built on, and it damaged the cells of every one. The bacteria that break down grass fibre wouldn’t grow in its presence at all.

So they defend themselves the only way open to them. They saturate it, adding hydrogen across the double bonds until the fat is stable and harmless to them. On most diets they get through 70% to 95% of the linoleic acid and 85% to 100% of the linolenic before anything leaves the rumen.

That is why ruminant fat looks and behaves the way it does. Beef dripping is around half saturated and about 4% polyunsaturated, firm on the shelf and unbothered by a hot pan. Lard, from the pig, comes in near 11% polyunsaturated. Chicken fat is nearer 21%.

Finish a steer on grain for his last few months and the rumen does the same job on that. The fat still comes out overwhelmingly saturated and monounsaturated, and what grass adds on top is more omega-3 and more CLA. Grass-fed against grain-fed goes through the difference line by line.

The saturating leaves fingerprints, too. Conjugated linoleic acid and vaccenic acid are half-finished fats from the process, and beef, lamb, milk and butter are their main natural source in the human diet.

The pig and the chicken are whatever was in the trough

A pig has one simple stomach, much like yours, and so does a chicken, give or take a gizzard. Neither has a vat, neither can do much with grass, and neither has any way of saturating the fat that arrives in its feed.

A modern pig or broiler eats cereals and soya meal from crops grown on ploughed land, and the polyunsaturated fat in that ration is laid down in the pork belly and the chicken skin much as it arrived. The chicken breast avoids the problem by containing almost no fat at all, which is a problem of its own. Pork and chicken each earn a place on a carnivore plate, a rung below, and their own pages say where.

Most of what farm animals eat was never human food in the first place. In 2017 the UN’s Food and Agriculture Organization, the same body that published Livestock’s Long Shadow in 2006, worked through what the world’s livestock actually eat and found that 86% of it is material people don’t eat: grass, leaves, crop residues and the leftovers from feeding ourselves. Grazing cattle take in around 0.6 kg of human-edible protein for every kilo of protein they hand back as meat and milk. On the same sums, pigs and poultry eat more human-edible protein than they return.

A study of British systems at Nottingham landed in the same place. Once only the feed a person could have eaten was counted, grass-finished upland suckler beef and lowland lamb beat pig and poultry meat on efficiency, and upland suckler beef, along with milk, put more edible protein back than it took in.

Britain has been grazing these hills for 6,000 years

The first farmers crossed from the Continent around 4000 BC with cattle and sheep in their boats, which says something about what they felt could not be left behind.

The animals took to the place. The same wet Atlantic weather that has wrecked every bank holiday on record grows grass with real enthusiasm, from the Pennine tops down to the Somerset Levels, where fields spend the winter under water and a cereal crop would simply drown.

On the unfenced fells and commons, the flocks have been there so long they no longer need walls. A hill ewe learns the patch of mountain she was raised on, where the shelter is in a February gale and where the grass comes first in spring, and she teaches it to her lambs. Cumbrians call it a heft. In Wales it is the cynefin. Lake District farms pass a landlord’s flock from tenant to tenant so the knowledge is not lost, and when UNESCO made the Lake District a World Heritage Site in 2017, the hefted flocks were part of the reason. The families still working those hills, and the policy leaning on them, are the subject of British farming.

Beatrix Potter, remembered for a rabbit, spent the rabbit’s money on Lake District hill farms. She bred prize-winning Herdwicks, and in 1943 she became the first woman elected president of the Herdwick Sheep Breeders’ Association. She died that December before she could take the chair, and left some 4,000 acres to the National Trust on the condition that the fell farms keep pure Herdwick flocks. They still do.

The soil keeps its own record. In 1949 Rothamsted, the Hertfordshire research station that has been running field trials since the 1840s, ploughed up plots on a field that had been grazed grass since 1838 and put them into arable crops. The soil carbon went into a slide that took 50 years to bottom out, at the level of another field on the estate that had been under the plough for centuries.

One field of grass stocks the larder and the wardrobe

Most arguments about ruminants start and finish at the meat, which leaves out most of the animal and a good half of the carnivore food list.

The meat runs from shin to sirloin, and every British cut has its job. Keep a sheep for a few more years of grazing and the flavour deepens with each one, which is the case for mutton, the meat Britain ate for centuries and then quietly stopped buying.

A dairy cow turns grass into milk, and milk is where the rumen’s saturated fat gets poured into a jug. Drunk the way it comes out of her, it is a whole food in the oldest sense of the phrase, and raw milk has a page of its own.

Skim the cream and churn it and you have butter: around four-fifths fat, close to two-thirds of that saturated, solid on a cold table and the reason margarine needed an advertising budget. Butter was always worth taking.

Add rennet to milk and you have the beginnings of cheese. Traditional rennet comes from the abomasum of a young calf, the fourth chamber of that one stomach, doing one last job. Britain now makes more than 700 named cheeses from the milk of cows, ewes, goats and even buffalo, which are ruminants as well.

Render the hard fat from around the kidneys and you get tallow. It lit British homes as candles and scrubbed them as soap, and it still fries the chips in plenty of shops across the north. Rendering your own needs a pan, some suet and a little patience.

Shear the sheep and the fleece clothed the country and paid for a good deal of it. Wool was England’s great medieval export, and the Lord Speaker still sits on the Woolsack, a seat that goes back to the 14th century.

Tan the hide and you have leather, which was boots, saddles, harness and fire buckets for centuries before anybody had heard of plastic.

And whatever the animal can’t use goes back on the field as muck, returning the minerals the grass pulled up to the ground they came from, with dung beetles and earthworms on hand to dig it in.

The cow belches methane, and the carbon in it was grass last summer

Archaea in the rumen make that methane, mopping up the hydrogen left over from fermentation, and it leaves by the front end, whatever the jokes say.

The carbon in it came out of the air, by way of the grass, in the months before. Once belched, methane breaks down in the atmosphere in about 12 years into carbon dioxide and water, which the grass draws back in. A herd that holds its size holds that methane level steady, topping up a stock that drains away at the other end.

Fossil carbon runs the other way. It comes out of the ground once, after millions of years locked away, and stays in circulation for centuries.

Britain’s herd and flock have been shrinking for years. The UK sheep flock hit its lowest recorded level in 2024 and fell again in 2025, and England’s cattle herd is now the smallest since the June survey’s current series began in 1984. The Climate Change Committee still wants 27% fewer cattle and sheep by 2040, with the land handed over to trees and bog.

The full fight, figure by figure, is in cattle farming myths and the cow apocalypse.

The hill is still doing its job

Nobody on the Berwyn has briefed the ewe. By October her lamb will be weaned and gone down the valley, and the grass will be greener wherever the pair of them have been. What these islands have made of that work in the kitchen, from the Sunday joint to the dripping tin, is laid out on The British Table.

She’ll be back on the same patch of mountain tomorrow, on a path her mother showed her.