Domestic Pig (Sus domesticus): Facts, Intelligence and Diet

What is a pig and where does it come from?

Pigs belong to the family Suidae, which also includes the wild boar, warthogs, babirusas and bush pigs. The domestic pig’s ancestor is the wild boar (Sus scrofa), which still roams forests from western Europe to Japan. Because domestic pigs and wild boar interbreed freely, many scientists treat the pig as a subspecies, Sus scrofa domesticus. Others, including the American Society of Mammalogists, list it as a separate species, Sus domesticus, so both names are in use.

Archaeology and genetics show that pigs were domesticated at least twice. The first center was the Near East, around the upper Tigris basin in what is now southeastern Turkey and northern Iraq, where people were managing wild boar more than 10,000 years ago. A second, independent domestication happened in China about 8,000 years ago.

Pigs from the Near East reached Europe at least 8,500 years ago with early farmers. Over the following centuries they mated so often with local wild boar that modern European pigs carry very little Near Eastern ancestry, even though they kept their tame, domestic traits. In the 18th and 19th centuries, British breeders crossed European pigs with Chinese pigs, which matured faster and had larger litters. Many modern breeds still carry this Asian heritage.

Appearance and senses

A pig has a long, heavy body, short legs and a large head ending in a flat, round snout. The snout is strengthened by a special bone, the prenasal bone, and tipped with a tough disk of cartilage. It works both as a digging tool and as a sense organ packed with touch receptors. Each foot has four toes; pigs walk on the two large middle hooves, and the two smaller outer toes help on soft ground.

Most pigs have a thin coat of coarse bristles, so their skin shows through. Color depends on breed: pink and white in Large White and Landrace pigs, ginger-red in the Tamworth, black in the Large Black and Iberian pig, and black with a white band in the Hampshire and Saddleback. The Mangalica of Hungary grows a thick, curly woolly coat. Adult pigs have 44 teeth, and males grow sharp, continuously growing canine tusks, although farm piglets often have their needle teeth clipped.

Smell is the pig’s most important sense. The pig genome contains more than 1,100 genes for smell receptors, slightly more than the dog’s, and in France and Italy pigs have long been used to sniff out truffles underground. Pigs identify one another mainly by scent and voice. Their eyes are set on the sides of the head, giving a panoramic field of view of about 310 degrees. Pigs have two kinds of color-sensitive cone cells, so they probably see a limited range of colors.

How big do pigs get?

Size varies greatly by breed and by whether a pig is allowed to reach maturity. Adult farm pigs generally weigh 140–300 kg (310–660 lb), and mature breeding boars of large breeds can weigh more. Most pigs never reach adult size, because market pigs are slaughtered when they weigh roughly 100–135 kg (220–300 lb).

Miniature breeds are much smaller. The Göttingen minipig, bred for research, typically weighs around 26 kg (57 lb) when fully grown, while pet pot-bellied pigs often reach 40–70 kg (90–150 lb). The heaviest pig on record was Big Bill, a Poland China hog from Tennessee that weighed 1,157 kg (2,552 lb) in 1933. Weights for different types of pigs are compared in How much does a pig weigh?.

Habitat and range

Pigs are kept on every inhabited continent. China has by far the most, followed by the European Union, the United States and Brazil. They are rare in countries where religious rules forbid eating pork, which is the case in Judaism and Islam.

Many pigs live indoors on large commercial farms. Others are raised outdoors on pasture or in woodland, the traditional way of keeping pigs in Europe for thousands of years. In Spain and Portugal, Iberian pigs still graze in oak woodland called dehesa or montado, where they fatten on fallen acorns in autumn.

Pigs readily return to the wild. European explorers brought pigs to the Americas from the late 15th century onward, and Polynesian voyagers carried them across the Pacific long before that. Feral pigs, and hybrids between pigs and introduced wild boar, now live in much of the southern United States, Australia, New Zealand, Hawaii and South America. There they dig up native plants, compete with wildlife and damage crops, which makes them one of the most troublesome invasive mammals in the world.

Diet and rooting

Pigs are true omnivores. Given the chance, free-ranging pigs eat roots, bulbs, tubers, grasses, leaves, nuts, acorns, fruit and fungi, along with earthworms, insect larvae, snails, small animals, eggs and carrion. On commercial farms, they are fed carefully balanced rations based mainly on grains such as corn, wheat and barley, plus soybean meal.

Rooting is the pig’s signature behavior. A pig pushes its snout into the soil and uses its powerful neck to plow up the ground, smelling and feeling for food as it goes. Piglets begin this nudging behavior from birth, when they push at their mother’s udder to start the milk flowing. Pigs are strongly motivated to root even when they are well fed, and outdoor pigs can turn a grassy field into bare earth in a few weeks.

Free-ranging pigs often walk several kilometers a day while foraging. Unlike cattle and sheep, pigs have a simple stomach, not a multi-chambered one, so they digest food more like people do and cannot live on grass alone.

Behavior and intelligence

Pigs are social animals. In natural conditions, they live in small groups of a few related sows and their young, while adult males mostly live alone and join the group to breed. Group members keep in touch with grunts and squeals, huddle together to rest and settle disputes with a pecking order that forms quickly through pushing and biting.

Pigs are also notably clean in their habits when they have space. They choose separate places to sleep, feed and dung, keeping the dunging area well away from the nest. Rolling in mud, which gave pigs their dirty reputation, is actually a way of cooling down, because pigs have very few working sweat glands. This is explained in detail in Do pigs sweat?.

Research has shown that pigs are among the most intelligent domestic animals. In one experiment, pigs that had become used to a mirror used it to find food hidden behind a barrier. Others learned to move a cursor on a screen with a joystick held in their snouts, and pigs can follow a human’s pointing gesture to find a reward. Pigs remember where food was hidden, recognize individual pigs and people, and appear to change their foraging tactics when a rival is following them. The evidence is explored in How smart are pigs?.

Reproduction and piglets

Female pigs, called gilts until they have their first litter, can breed from about five to eight months old, and they come into heat about every three weeks. Pregnancy lasts about 114 days, often remembered as “three months, three weeks and three days.”

Shortly before giving birth, a sow left to herself will leave the group and build a nest. She digs a hollow and piles it with grass, twigs and branches, and she gives birth lying down, unusual among hoofed mammals. Modern farm breeds commonly have about 10–14 piglets in a litter, two or three times as many as a wild boar sow. Each piglet weighs about 1–1.5 kg (2.2–3.3 lb) at birth.

Within hours, piglets fight over the front teats, which give the most milk, and each piglet then keeps to its own teat, a pattern called the teat order. The sow grunts in a steady rhythm while she nurses, and her grunting speeds up just before the milk lets down. Left to themselves, sows wean their piglets gradually at around three to four months, but on most farms piglets are weaned at three to four weeks old.

Male pigs are boars, castrated males are barrows, young pigs are piglets and a group of piglets born together is a litter. Giving birth is called farrowing.

How long do pigs live?

A domestic pig that is allowed to grow old commonly lives about 15–20 years, and the recorded maximum is about 27 years. The oldest pig recognized by Guinness World Records, Baby Jane of Illinois, died in 2021 aged 23 years and 221 days.

Farm pigs live much shorter lives. Pigs raised for pork are usually slaughtered at about five to seven months old, and breeding sows are commonly replaced after a few litters, at around two to four years old. Wild boar rarely survive more than a few years in the wild. The full picture is in How long do pigs live?.

Pigs and people

Pork is one of the two most widely eaten meats in the world, alongside chicken, and about 1.5 billion pigs are slaughtered every year. Pigs also provide leather and bristles, and because their organs are similar in size and function to ours, pig heart valves have long been used in human heart surgery.

Pigs have been part of human culture for millennia. The pig is one of the 12 animals of the Chinese zodiac, and pigs appear in stories from George Orwell’s Animal Farm to Charlotte’s Web and the British cartoon Peppa Pig. Some pigs are kept as pets, although many “mini pigs” grow far larger than their owners expect.

Many traditional breeds have become rare as farms switched to a few high-production breeds. The Livestock Conservancy in the United States lists the Choctaw hog, the Mulefoot and the Ossabaw Island hog among the rarest, and breed societies in Britain work to protect old breeds such as the Tamworth and the British Lop.

Myths and facts

Myth: pigs are dirty animals. Given room, pigs keep a clean nest and dung well away from it. Wallowing in mud is a cooling strategy and also helps protect the skin from sunburn and insects.

Myth: pigs “sweat like a pig.” Pigs have very few functional sweat glands and cannot cool themselves by sweating, which is why they need water or mud on hot days.

Fact: pigs are surprisingly resistant to some snake venoms. Pigs carry a change in a muscle receptor that makes it harder for certain snake neurotoxins to bind, a trait they share with mongooses, honey badgers and hedgehogs. They are not fully immune, however.