The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus ''
Sus'', is an
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
,
domesticated
Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A ...
,
even-toed, hoofed mammal. It is variously considered a
subspecies of ''Sus scrofa'' (the
wild boar
The wild boar (''Sus scrofa''), also known as the wild swine, common wild pig, Eurasian wild pig, or simply wild pig, is a suid native to much of Eurasia and North Africa, and has been introduced to the Americas and Oceania. The species is ...
or Eurasian boar) or a distinct
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
. The pig's head-plus-body length ranges from , and adult pigs typically weigh between , with well-fed individuals even exceeding this range. The size and weight of hogs largely depends on their breed. Compared to other
artiodactyl
The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
s, a pig's head is relatively long and pointed. Most even-toed ungulates are
herbivorous
A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
, but pigs are omnivores, like their wild relative. Pigs grunt and make snorting sounds.
When used as
livestock
Livestock are the domesticated animals raised in an agricultural setting to provide labor and produce diversified products for consumption such as meat, eggs, milk, fur, leather, and wool. The term is sometimes used to refer solely to animal ...
, pigs are
farmed primarily for the production of meat, called
pork
Pork is the culinary name for the meat of the domestic pig (''Sus domesticus''). It is the most commonly consumed meat worldwide, with evidence of pig husbandry dating back to 5000 BCE.
Pork is eaten both freshly cooked and preserved; ...
. A group of pigs is called a ''passel'', a ''team'', or a ''sounder''. The animal's bones, hide, and
bristles
A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, a plant, or on a tool such as a brush or broom.
Synthetic types
Synthetic materials such as nylon are also used to make bristles in items such as br ...
are also used in products. Pigs, especially
miniature
A miniature is a small-scale reproduction, or a small version. It may refer to:
* Portrait miniature, a miniature portrait painting
* Miniature art, miniature painting, engraving and sculpture
* Miniature (chess), a masterful chess game or probl ...
breeds, are kept
as pets.
Biology
![Pig hand skeleton](https://upload.wikimedia.org/wikipedia/commons/5/56/Pig_hand_skeleton.jpg)
The pig typically has a large head, with a long snout which is strengthened by a special prenasal bone and a disk of
cartilage at the tip.
The snout is used to dig into the soil to find food and is a very acute sense organ. The
dental formula
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...
of adult pigs is , giving a total of 44
teeth
A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...
. The rear teeth are adapted for crushing. In the male, the canine teeth can form
tusk
Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share ...
s, which grow continuously and are sharpened by constantly being ground against each other.
Four
hoof
The hoof (plural: hooves) is the tip of a toe of an ungulate mammal, which is covered and strengthened with a thick and horny keratin covering. Artiodactyls are even-toed ungulates, species whose feet have an even number of digits, yet the rum ...
ed toes are on each foot, with the two larger central toes bearing most of the weight, but the outer two also being used in soft ground.
Most pigs have rather a
bristle
A bristle is a stiff hair or feather (natural or artificial), either on an animal, such as a pig, a plant, or on a tool such as a brush or broom.
Synthetic types
Synthetic materials such as nylon are also used to make bristles in items such as ...
d sparse hair covering on their skin, although
wool
Wool is the textile fibre obtained from sheep and other mammals, especially goats, rabbits, and camelids. The term may also refer to inorganic materials, such as mineral wool and glass wool, that have properties similar to animal wool. ...
ly-coated breeds such as the
Mangalitsa
The Mangalica (also Mangalitsa or Mangalitza) is a Hungarian breed of domestic pig. It was developed in the mid-19th century by crossbreeding breeds from the nearby Romanian Salonta (Hungarian: ''Nagyszalonta'', colloquially ''Szalonta ...
exist.
Pigs possess both
apocrine
Apocrine () glands are a type of exocrine gland, which are themselves a type of gland, i.e. a group of cells specialized for the release of secretions. Exocrine glands secrete by one of three means: holocrine, merocrine and apocrine. In apocri ...
and
eccrine sweat glands, although the latter appear limited to the snout and dorsonasal areas.
Pigs, however, like other "hairless" mammals (e.g. elephants, rhinos, and mole-rats), do not use thermal sweat glands in cooling.
Pigs are also less able than many other mammals to dissipate heat from wet
mucous membrane
A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue. It i ...
s in the mouth through panting. Their
thermoneutral zone is . At higher temperatures, pigs lose heat by
wallowing Wallowing in animals is comfort behaviour during which an animal rolls about or lies in mud, water or snow. Some definitions include rolling about in dust, however, in ethology this is usually referred to as dust bathing. Wallowing is often com ...
in mud or water via evaporative cooling, although it has been suggested that wallowing may serve other functions, such as protection from sunburn,
ecto-parasite control, and scent-marking.
Pigs are one of four known mammalian species which possess mutations in the
nicotinic acetylcholine receptor
Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ner ...
that protect against snake venom.
Mongoose
A mongoose is a small terrestrial carnivorous mammal belonging to the family Herpestidae. This family is currently split into two subfamilies, the Herpestinae and the Mungotinae. The Herpestinae comprises 23 living species that are native to so ...
s,
honey badger
The honey badger (''Mellivora capensis''), also known as the ratel ( or ), is a mammal widely distributed in Africa, Southwest Asia, and the Indian subcontinent. Because of its wide range and occurrence in a variety of habitats, it is liste ...
s,
hedgehog
A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introductio ...
s, and pigs all have modifications to the receptor pocket which prevents the
snake venom α-neurotoxin from binding. These represent four separate, independent mutations.
Pigs have small lungs in relation to their body size, and are thus more susceptible than other domesticated animals to fatal
bronchitis
Bronchitis is inflammation of the bronchi (large and medium-sized airways) in the lungs that causes coughing. Bronchitis usually begins as an infection in the nose, ears, throat, or sinuses. The infection then makes its way down to the bronchi. ...
and
pneumonia
Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severi ...
. Pigs have a
maximum life span
Maximum life span (or, for humans, maximum reported age at death) is a measure of the maximum amount of time one or more members of a population have been observed to survive between birth and death. The term can also denote an estimate of the m ...
of about 27 years.
Genetics and genomics
The genome of the pig has been sequenced and contains about 22,342 protein-coding genes.
Taxonomy
The pig is most often considered to be a
subspecies of the
wild boar
The wild boar (''Sus scrofa''), also known as the wild swine, common wild pig, Eurasian wild pig, or simply wild pig, is a suid native to much of Eurasia and North Africa, and has been introduced to the Americas and Oceania. The species is ...
, which was given the name ''Sus scrofa'' by
Carl Linnaeus
Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
in 1758; following from this, the formal name of the pig is ''Sus scrofa domesticus''.
However, in 1777,
Johann Christian Polycarp Erxleben
Johann Christian Polycarp Erxleben was a German naturalist from Quedlinburg.
Erxleben was professor of physics and veterinary medicine at the University of Göttingen
The University of Göttingen, officially the Georg August University of ...
classified the pig as a separate
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
from the wild boar. He gave it the name ''Sus domesticus'', which is still used by some taxonomists.
The
American Society of Mammalogists considers it a separate species.
History
![CapitalMuseum11](https://upload.wikimedia.org/wikipedia/commons/d/dc/CapitalMuseum11.jpg)
Archaeological evidence suggests that pigs were
domesticated
Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A ...
from wild boar in the
Near East in the
Tigris
The Tigris () is the easternmost of the two great rivers that define Mesopotamia, the other being the Euphrates. The river flows south from the mountains of the Armenian Highlands through the Syrian and Arabian Deserts, and empties into the ...
Basin,
Çayönü
Çayönü Tepesi is a Neolithic settlement in southeastern Turkey which prospered from circa 8,630 to 6,800 BC. It is located forty kilometres north-west of Diyarbakır, at the foot of the Taurus mountains. It lies near the Boğazçay, a trib ...
,
Cafer Höyük
Cafer Hoyuk or Cafer Höyük is an archaeological site located around northeast of Malatya, Turkey in the Euphrates valley. It was inhabited over ten thousand years ago during the Neolithic revolution.
Construction of the Karakaya Dam has floo ...
,
Nevalı Çori
Nevalı Çori ( tr, Nevali Çori, ku, Newala Çorî) was an early Neolithic settlement on the middle Euphrates, in Şanlıurfa Province, Southeastern Anatolia, Turkey. The site is known for having some of the world's oldest known temples and mon ...
being managed in the wild in a way similar to the way they are managed by some modern New Guineans. Remains of pigs have been dated to earlier than 11,400 years ago in
Cyprus
Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ge ...
. Those animals must have been introduced from the mainland, which suggests domestication in the adjacent mainland by then. Pigs were separately domesticated in China beginning 8,000 years ago, and have been one of the most important domesticated animal there ever since.
In the Near East, pig husbandry spread for the next few millennia. It reduced gradually during the
Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second prin ...
, as rural populations focused instead on commodity-producing livestock. It was sustained in urbanized regions, however.
DNA evidence from subfossil remains of teeth and jawbones of Neolithic pigs shows that the first domestic pigs in Europe had been brought from the Near East. This stimulated the domestication of local European wild boar, resulting in a third domestication event with the Near Eastern genes dying out in European pig stock. Modern domesticated pigs have involved complex exchanges, with European domesticated lines being exported, in turn, to the ancient Near East. Historical records indicate that Asian pigs were introduced into Europe during the 18th and early 19th centuries.
In August 2015, a study looked at over 100 pig genome sequences to ascertain their process of domestication, which was assumed to have been initiated by humans, involved few individuals, and relied on reproductive isolation between wild and domestic forms. The study found that the assumption of reproductive isolation with population bottlenecks was not supported. The study indicated that pigs were domesticated separately in Western Asia and China, with Western Asian pigs introduced into Europe, where they crossed with wild boar. A model that fit the data included a mixture with a now extinct
ghost population A ghost population is a population that has been inferred through using statistical techniques.
Population studies
In 2004, it was proposed that maximum likelihood or Bayesian approaches that estimate the migration rates and population sizes using ...
of wild pigs during the
Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
. The study also found that despite back-crossing with wild pigs, the genomes of domestic pigs have strong signatures of selection at DNA loci that affect behavior and morphology. The study concluded that human selection for domestic traits likely counteracted the homogenizing effect of gene flow from wild boars and created
domestication islands in the genome. The same process may also apply to other domesticated animals.
In 2019, a study showed that the pig had arrived in Europe from the Near East 8,500 years ago. Over the next 3,000 years they then admixed with the European wild boar until their genome showed less than 5% Near Eastern ancestry, yet retained their domesticated features.
Among the animals that the Spanish
introduced to the
Chiloé Archipelago
The Chiloé Archipelago ( es, Archipiélago de Chiloé, , ) is a group of islands lying off the coast of Chile, in the Los Lagos Region. It is separated from mainland Chile by the Chacao Channel in the north, the Sea of Chiloé in the east and t ...
in the 16th century, pigs were the most successful to adapt. The pigs benefited from abundant
shellfish and
algae exposed by the large
tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables ...
s of the archipelago.
Pigs were brought to southeastern North America from Europe by
de Soto De Soto commonly refers to
* Hernando de Soto (c. 1495 – 1542), Spanish explorer
* DeSoto (automobile), an American automobile brand from 1928 to 1961
De Soto, DeSoto, Desoto, or de Soto may also refer to:
Places in the United States of Ameri ...
and other early Spanish
explorer
Exploration refers to the historical practice of discovering remote lands. It is studied by geographers and historians.
Two major eras of exploration occurred in human history: one of convergence, and one of divergence. The first, covering most ...
s. Escaped pigs became
feral
A feral () animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some ...
and caused a great deal of disruption to
Native Americans.
Feral pig populations in the southeastern United States have since migrated north and are a growing concern in the
Midwest. Considered an invasive species, many state agencies have programs to trap or hunt feral pigs as means of removal. Domestic pigs have become feral in many other parts of the world (e.g. New Zealand and northern
Queensland
)
, nickname = Sunshine State
, image_map = Queensland in Australia.svg
, map_caption = Location of Queensland in Australia
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, establishe ...
) and have caused substantial environmental damage. Feral hybrids of the European wild boar with the domestic pig are also very disruptive to both environment and agriculture (among the 100 most damaging animal species), especially in southeastern South America from Uruguay to Brazil's
Mato Grosso do Sul and
São Paulo
São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the Ga ...
.
With around 1 billion individuals alive at any time, the
domesticated
Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A ...
pig is one of the most numerous large mammals on the planet.
Reproduction
Female pigs reach sexual maturity at 3–12 months of age and come into
estrus
The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous ...
every 18–24 days if they are not successfully bred. The variation in ovulation rate can be attributed to intrinsic factors such as age and genotype, as well as extrinsic factors like nutrition, environment, and the supplementation of exogenous hormones. The gestation period averages 112–120 days.
![Piglets IMG 5523](https://upload.wikimedia.org/wikipedia/commons/e/e5/Piglets_IMG_5523.jpg)
Estrus lasts two to three days, and the female's displayed receptiveness to mate is known as standing heat. Standing heat is a reflexive response that is stimulated when the female is in contact with the saliva of a sexually mature boar.
Androstenol
Androstenol, also known as 5α-androst-16-en-3α-ol (shortened to 3α,5α-androstenol or 3α-androstenol), is a 16-androstene class steroidal pheromone and neurosteroid in humans and other mammals, notably pigs. It possesses a characteristic musk ...
is one of the pheromones produced in the submaxillary salivary glands of boars that will trigger the female's response. The female cervix contains a series of five interdigitating pads, or folds, that will hold the boar's corkscrew-shaped penis during copulation. Females have
bicornuate uterus
A bicornuate uterus or bicornate uterus (from the Latin ''cornū'', meaning "horn"), is a type of mullerian anomaly in the human uterus, where there is a deep indentation at the fundus (top) of the uterus.
Pathophysiology
A bicornuate uterus ...
es and two conceptuses must be present in both uterine horns for pregnancy to be established. Maternal recognition of pregnancy in pigs occurs on days 11 to 12 of pregnancy and is marked by progesterone production from a functioning corpus luteum (CL). To avoid luteolysis by PGF2α, rescuing of the CL must occur via embryonic signaling of estradiol 17β and PGE2.
This signaling acts on both the endometrium and luteal tissue to prevent the regression of the CL by activation of genes that are responsible for CL maintenance. During mid to late pregnancy, the CL relies primarily on luteinizing hormone (LH) for maintenance until parturition.
Animal nutrition is important prior to reproduction and during gestation to ensure optimum reproductive performance is achieved.
Archeological evidence indicates that medieval European pigs farrowed, or bore a litter of piglets, once per year. By the nineteenth century, European piglets routinely double-farrowed, or bore two litters of piglets per year. It is unclear when this shift occurred.
Behavior
![Yorkshire pigs at animal sanctuary](https://upload.wikimedia.org/wikipedia/commons/2/2f/Yorkshire_pigs_at_animal_sanctuary.jpg)
In many ways pig behaviour appears to be intermediate between that of other
artiodactyls
The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
and of
carnivores
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other so ...
.
[Clutton-Brock, J., (1987). A Natural History of Domesticated Mammals. Cambridge University Press, Cambridge pp.73–74] Pigs seek out the company of other pigs and often huddle to maintain physical contact, although they do not naturally form large herds. They typically live in groups of about 8–10 adult sows, some young individuals, and some single males.
Because of their relative lack of sweat glands, pigs often control their body temperature using behavioural thermoregulation.
Wallowing Wallowing in animals is comfort behaviour during which an animal rolls about or lies in mud, water or snow. Some definitions include rolling about in dust, however, in ethology this is usually referred to as dust bathing. Wallowing is often com ...
, which often consists of coating the body with mud, is a behaviour frequently exhibited by pigs.
They do not submerge completely under the mud, but vary the depth and duration of wallowing depending on environmental conditions.
Typically, adult pigs start wallowing once the ambient temperature is around 17–21 °C (63–70 °F). They cover themselves from head to toe in mud.
Pigs may use mud as a sunscreen, or as a method of keeping parasites away.
Most bristled pigs will "blow their coat", meaning that they shed most of the longer, coarser stiff hair once a year, usually in spring or early summer, to prepare for the warmer months ahead.
If conditions permit, pigs feed continuously for many hours and then sleep for many hours, in contrast to
ruminants
Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...
which tend to feed for a short time and then sleep for a short time. Pigs are
omnivorous
An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nut ...
, and are highly versatile in their feeding behaviour. As they are foraging animals, they primarily eat leaves, stems, roots, fruits, and flowers. Pigs play an important role in regions where
pig toilet
A pig toilet (sometimes called a "pig sty latrine") is a simple type of dry toilet consisting of an outhouse mounted over a pigsty, with a chute or hole connecting the two. The pigs consume the feces of the users of the toilet, as well as other f ...
s are employed. Pigs are highly intelligent animals, on par with dogs, and according to David DiSalvo's writing in ''
Forbes
''Forbes'' () is an American business magazine owned by Integrated Whale Media Investments and the Forbes family. Published eight times a year, it features articles on finance, industry, investing, and marketing topics. ''Forbes'' also r ...
'', they are "widely considered the smartest domesticated animal in the world. Pigs have demonstrated the ability to move a cursor on a
video screen with their snouts and understand what is happening onscreen, and have learned to distinguish between the scribbles they had seen before and those they were seeing for the first time."
Rooting
![JulianaPigletPlaytimeCropped&Resized](https://upload.wikimedia.org/wikipedia/commons/0/03/JulianaPigletPlaytimeCropped%26Resized.gif)
Rooting is an instinctual behavior in pigs that is characterized by a pig nudging its snout into something. Similar to a
cat's kneading, rooting is found comforting. It first happens when piglets are born to obtain their mother's milk, and can become a habitual, obsessive behavior which is most prominent in animals
weaned
Weaning is the process of gradually introducing an infant human or another mammal to what will be its adult diet while withdrawing the supply of its mother's milk.
The process takes place only in mammals, as only mammals produce milk. The infan ...
too early.
Often, pigs will root and dig into the ground to forage for food.
By means of rooting, pigs have been used to
till
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
farmland.
Rooting is known to also be used as a means of communication.
Nose rings that pierce the septum of the nose discourage rooting because they make the behavior painful.
The breed known as the
kunekune
The Kunekune or is a small breed of domestic pig from New Zealand. Kunekune are hairy with a rotund build, and may bear wattles hanging from their lower jaws. Their colour ranges from black and white, to ginger, cream, gold-tip, black, brown, ...
hardly ever roots, as it can sustain itself by feeding on nothing other than grass. Not having to root around in the soil to find underground food (e.g. tubers), it thus has evolved to, for the most part, not possess the instinct for rooting.
Nest-building
A behavioural characteristic of pigs which they share with carnivores is
nest-building. Sows root in the ground to create depressions and then build nests in which to give birth. First, the sow digs a depression about the size of her body. She then collects twigs and leaves, and carries these in her mouth to the depression, building them into a mound. She distributes the softer, finer material to the centre of the mound using her feet. When the mound reaches the desired height, she places large branches, up to 2 metres in length, on the surface. She enters into the mound and roots around to create a depression within the gathered material. She then gives birth in a lying position, which, again, is different from other artiodactyls, which usually give birth in a standing position.
Nest-building behaviour is an important part in the process of pre and post-partum maternal behaviour. Nest-building will occur during the last 24 hours before the onset of farrowing and becomes most intense during 12 to 6 hours before farrowing.
Nest-building is divided into two phases: one of which is the initial phase of rooting in the ground while the second phase is the collecting, carrying and arranging of the nest material.
The sow will separate from the group and seek a suitable nest site with some shelter from rain and wind that has well-drained soil. This nest-building behaviour is performed to provide the offspring with shelter, comfort, and thermoregulation. The nest will provide protection against weather and predators while keeping the piglets close to the sow and away from the rest of the herd. This ensures they do not get trampled on and that other piglets are not stealing milk from the sow.
Nest-building can be influenced by internal and external stimuli. Internal hormonal changes and the completion of one nesting phase are indicators of this maternal behaviour.
The onset is triggered by the rise in prolactin levels, which is caused by a decrease in progesterone and an increase in prostaglandin, while the gathering of the nest material seems to be regulated more by external stimuli such as temperature.
The longer time spent on nest-building will increase pre-partum oxytocin.
Nursing and suckling behaviour
![Two domestic piglets suckling](https://upload.wikimedia.org/wikipedia/commons/8/87/Two_domestic_piglets_suckling.jpg)
Pigs display complex nursing and suckling behaviour.
Nursing occurs every 50–60 minutes, and the sow requires stimulation from piglets before milk let-down. Sensory inputs (vocalisation, odours from mammary and birth fluids, and hair patterns of the sow) are particularly important immediately post-birth to facilitate teat location by the piglets.
Initially, the piglets compete for position at the udder; then the piglets massage around their respective teats with their snouts, during which time the sow grunts at slow, regular intervals. Each series of grunts varies in frequency, tone and magnitude, indicating the stages of nursing to the piglets.
The phase of competition for teats and of nosing the udder lasts for about one minute and ends when milk flow begins. In the third phase, the piglets hold the teats in their mouths and suck with slow mouth movements (one per second), and the rate of the sow's grunting increases for approximately 20 seconds. The grunt peak in the third phase of suckling does not coincide with milk ejection, but rather the release of oxytocin from the pituitary into the bloodstream.
Phase four coincides with the period of main milk flow (10–20 seconds) when the piglets suddenly withdraw slightly from the udder and start sucking with rapid mouth movements of about three per second. The sow grunts rapidly, lower in tone and often in quick runs of three or four, during this phase. Finally, the flow stops and so does the grunting of the sow. The piglets may then dart from teat to teat and recommence suckling with slow movements, or nosing the udder. Piglets massage and suckle the sow's teats after milk flow ceases as a way of letting the sow know their nutritional status. This helps her to regulate the amount of milk released from that teat in future sucklings. The more intense the post-feed massaging of a teat, the greater the future milk release from that teat will be.
Teat order
![PigCochon allaitant](https://upload.wikimedia.org/wikipedia/commons/b/bf/PigCochon_allaitant.jpg)
In pigs,
dominance hierarchies can be formed at a very early age. Piglets are highly precocious and within minutes of being born, or sometimes seconds, will attempt to suckle. The piglets are born with sharp teeth and fight to develop a teat order as the
anterior teats produce a greater quantity of milk. Once established, this teat order remains stable with each piglet tending to feed on a particular teat or group of teats.
Stimulation of the anterior teats appears to be important in causing milk letdown,
so it might be advantageous to the entire litter to have these teats occupied by healthy piglets.
Using an artificial sow to rear groups of piglets, recognition of a teat in a particular area of the udder depended initially on visual orientation by means of reference points on the udder to find the area, and then the olfactory sense for the more accurate search within that area.
Senses
Pigs have
panoramic vision of approximately 310° and
binocular vision
In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
of 35° to 50°. It is thought they have no
eye accommodation. Other animals that have no accommodation, e.g. sheep, lift their heads to see distant objects. The extent to which pigs have colour vision is still a source of some debate; however, the presence of
cone cells in the retina with two distinct wavelength sensitivities (blue and green) suggests that at least some colour vision is present.
Pigs have a well-developed sense of smell, and use is made of this in Europe where they are trained to locate underground
truffles
A truffle is the fruiting body of a subterranean ascomycete fungus, predominantly one of the many species of the genus ''Tuber''. In addition to ''Tuber'', many other genera of fungi are classified as truffles including '' Geopora'', '' Pe ...
. Olfactory rather than visual stimuli are used in the identification of other pigs.
[Houpt, K.A., (1998). Domestic Animal Behavior for Veterinarians and Animal Scientists. 3rd edition. Iowa State University Press, Ames.] Hearing is also well developed, and localisation of sounds is made by moving the head. Pigs use auditory stimuli extensively as a means of communication in all social activities.
[Gonyou, H.W., (2001). The social behaviour of pigs. In "Social Behaviour in Farm Animals", eds. Keeling, L.J., and Gonyou, H.W. CABI, Oxford.] Alarm or aversive stimuli are transmitted to other pigs not only by auditory cues but also by
pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s.
Similarly, recognition between the sow and her piglets is by olfactory and vocal cues.
Breeds
Many
breeds of pig exist, with different colors, shapes, and sizes. According to
The Livestock Conservancy
The Livestock Conservancy, formerly known as the American Livestock Breeds Conservancy (ALBC) and prior to that, the American Minor Breeds Conservancy, is a nonprofit organization focused on preserving and promoting rare breeds, also known as "h ...
, as of 2016, three breeds of pig are critically rare (having a global population of fewer than 2000). They are the
Choctaw hog, the
Mulefoot, and the
Ossabaw Island hog. The smallest known pig breed in the world is the
Göttingen minipig
The Göttingen minipig (also known as the ''Göttinger'' or "Goettingen" minipig) is a breed of small swine. The Göttingen minipig is the smallest domestic pig breed known in the world; as an adult, they weigh around . Beside being known for the ...
, typically weighing about as a healthy, full-grown adult.
In agriculture
When in use as livestock, the pig is mostly farmed for its meat, pork. Other food products made from pigs include pork
sausage
A sausage is a type of meat product usually made from ground meat—often pork, beef, or poultry—along with salt, spices and other flavourings. Other ingredients, such as grains or breadcrumbs may be included as fillers or extenders.
...
(which includes
casings that are made from the
intestines),
bacon,
gammon,
ham
Ham is pork from a leg cut that has been preserved by wet or dry curing, with or without smoking."Bacon: Bacon and Ham Curing" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 39. As a processed meat, the term "ham ...
and
pork rinds
Pork rind is the culinary term for the skin of a pig. It can be used in many different ways.
It can be rendered, fried in fat, baked, or roasted to produce a kind of pork cracklings (US) or scratchings (UK); these are served in small piece ...
. The head of a pig can be used to make a preserved jelly called
head cheese
Head cheese (Dutch: ''hoofdkaas'') or brawn is a cold cut terrine or meat jelly that originated in Europe. It is made with flesh from the head of a calf or pig (less commonly a sheep or cow), typically set in aspic, and usually eaten cold, ...
, which is sometimes known as brawn.
Liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
,
chitterlings,
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
(for
black pudding
, type =
, course =
, place_of_origin = Great Britain and Ireland
, region =England, Ireland, Scotland
, associated_cuisine = United Kingdom and Ireland
, creator =
, year =
, mintime =
, maxtime =
, served = Hot, occasionally ...
), and other
offal
Offal (), also called variety meats, pluck or organ meats, is the organs of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but usually excludes muscle. Offal may also refe ...
from pigs are also widely used for food. In some religions, such as
Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in t ...
and
Islam, pork is a
taboo food. Approximately 1.5 billion pigs are slaughtered each year for meat.
The use of
pig milk for human consumption does take place, but as there are certain difficulties in obtaining it, there is little commercial production.
Livestock pigs are exhibited at
agricultural show
An agricultural show is a public event exhibiting the equipment, animals, sports and recreation associated with agriculture and animal husbandry. The largest comprise a livestock show (a judged event or display in which breeding stock is exhibit ...
s, judged either as
stud stock compared to the standard features of each pig breed, or in commercial classes where the animals are judged primarily on their suitability for slaughter to provide premium meat.
The
skin of pigs is
eaten and used to produce seat covers, apparel, and other items.
In some
developing and
developed nation
A developed country (or industrialized country, high-income country, more economically developed country (MEDC), advanced country) is a sovereign state that has a high quality of life, developed economy and advanced technological infrastruct ...
s, the pig is usually raised outdoors in yards or fields. In some areas, pigs are allowed to
forage
Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used ...
in woods where they may be taken care of by
swineherds. In industrialized nations such as the United States, pig farming has switched from the
traditional pig farm to large-scale
intensive pig farms. This has resulted in lower production costs but can cause significant
cruelty
Cruelty is the pleasure in inflicting suffering or inaction towards another's suffering when a clear remedy is readily available. Sadism can also be related to this form of action or concept. Cruel ways of inflicting suffering may involve ...
problems. As consumers have become concerned with the humane treatment of livestock, demand for pasture-raised pork in these nations has increased.
As pets
Vietnamese pot-bellied pigs, a
miniature breed of pig, have made popular pets in the United States, beginning in the latter half of the 20th century.
In many respects, pot-bellied pigs are desirable and entertaining pets. They are considered intelligent, gregarious, and trainable. They lack the genetic hereditary weaknesses which commonly afflict certain pedigree cat and dog breeds, are generally quite sturdy, and have a reasonably affordable diet despite requiring large quantities of food. However, they can be strong-willed, defiant, and independent pets which will sometimes defy training. They require access to an outdoor space at all times, and depending on the individual pig, may become housebroken easily or never settle indoors. While hardy, an injured or sick pig will require costly surgery or larger than average quantities of medicine than most pets.
Pigs are highly intelligent, social creatures. They are considered
hypoallergenic
Hypoallergenic, meaning "below average" or "slightly" allergenic, is a term meaning that something (usually cosmetics, pets, textiles, food, etc.) causes fewer allergic reactions. The term was first used in 1953 in an advertising campaign for cos ...
, and are known to do quite well with people who have the usual animal allergies. Since these animals are known to have a life expectancy of 15 to 20 years, they require a long-term commitment.
Given pigs are bred primarily as livestock and have not been bred as companion animals for very long, selective breeding for a placid or biddable temperament is not well established. Pigs have radically different psychology to dogs and exhibit fight-or-flight instincts, independent nature, and natural assertiveness which can manifest as aggression towards children and a tendency to panic and lash out with little warning. Cats generally are safe around pigs as neither species has an incentive to express aggression or fear towards the other, although dogs will view pigs as prey animals and in turn, pigs will challenge dogs for food, leading to very violent fights.
Care
Male and female swine that have not been de-sexed may express unwanted aggressive behavior, and are prone to developing serious health issues. Regular trimming of the hooves is necessary; hooves left untreated cause major pain in the pig, can create malformations in bone structure and may cause the pig to be more susceptible to fungal growth between crevices of the hoof, or between the cracks in a split hoof. Male pigs, especially when left unaltered, can grow large, sharp tusks which may continue growing for years. Domestic owners may wish to keep their pigs' tusks trimmed back, or have them removed entirely.
As prey animals, pigs' natural instinctive behavior causes them to have a strong fear of being picked up, resulting in the animal expressing stress through struggling and squealing, but they will usually calm down once placed back onto the ground. This instinctual fear may be lessened if the pig has been frequently held since infancy. When holding pigs, supporting them under the legs makes being held not as stressful for the animal. Pigs need enrichment activities to keep their intelligent minds occupied; if pigs get bored, they often become destructive. As
rooting is found to be comforting, pigs kept in the house may root household objects, furniture or surfaces. While some owners are known to
pierce their pigs' noses to discourage rooting behaviour, the efficacy and humaneness of this practice is questionable. Pet pigs should be let outside daily to allow them to fulfill their natural desire of rooting around.
In human medical applications
Pigs, both as live animals and a source of post-mortem tissues, are one of the most valuable animal models used in biomedical research today, because of their biological, physiological, and anatomical similarities to human beings.
[ For instance, human skin is very similar to the pigskin, therefore pigskin has been used in many preclinical studies.] Porcine are used in finding treatments, cures for diseases, xenotransplantation, and for general education. They are also used in the development of medical instruments and devices, surgical techniques and instrumentation, and FDA-approved research. These animals contribute to the reduction methods for animal research, as they supply more information from fewer animals used, for a lower cost.
Xenotransplantation
Pigs are currently thought to be the best non-human candidates for organ donation
Organ donation is the process when a person allows an organ of their own to be removed and transplanted to another person, legally, either by consent while the donor is alive or dead with the assent of the next of kin.
Donation may be for re ...
to humans, and to date they are the only animal that has successfully donated an organ to a human body. The first successful donation of a non-human organ to a human body was conducted on 15 September 2021, when a kidney from a pig was transplanted to a brain-dead human and immediately started functioning similarly to a human kidney. The procedure, led by Dr. Robert Montgomery, used a donor pig that was genetically engineered to not have a specific carbohydrate that the human body considers a threat–Galactose-alpha-1,3-galactose
Galactose-''alpha''-1,3-galactose, commonly known as alpha gal and the Galili antigen, is a carbohydrate found in most mammalian cell membranes. It is not found in catarrhines, including humans, who have lost the GGTA1 gene. Their immune systems ...
. This followed an earlier major breakthrough when the carbohydrate was removed from genetically engineered mice.
Besides similarity between pig and human organs, pigs are among the best animals suited for human donation due the lower risk of cross-species disease transmission. This is caused by pigs' increased phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
distance from humans. Furthermore, they are readily available, and new infectious agents are less likely since they have been in close contact with humans through domestication for many generations.[Taylor, L. (2007]
Xenotransplantation
Emedicine.com
Some obstacles to successful organ donation from a pig to a human arise from the response of the recipient's immune system
The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splint ...
—generally more extreme than in allotransplantation
Allotransplant (''allo-'' meaning "other" in Greek) is the transplantation of cells, tissues, or organs to a recipient from a genetically non-identical donor of the same species. The transplant is called an allograft, allogeneic transplant, ...
s, ultimately results in rejection of the xenograft
Xenotransplantation (''xenos-'' from the Greek meaning "foreign" or strange), or heterologous transplant, is the transplantation of living cells, tissues or organs from one species to another. Such cells, tissues or organs are called xenograf ...
, and in some cases results in the death of the recipient—including hyperacute rejection, acute vascular rejection, cellular rejection, and chronic rejection.
Examples of viruses carried by pigs include porcine herpesvirus
''Herpesviridae'' is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word ''ἕρπειν ...
, rotavirus
''Rotavirus'' is a genus of double-stranded RNA viruses in the family ''Reoviridae''. Rotaviruses are the most common cause of diarrhoeal disease among infants and young children. Nearly every child in the world is infected with a rotavirus ...
, parvovirus
Parvoviruses are a family of animal viruses that constitute the family ''Parvoviridae''. They have linear, single-stranded DNA (ssDNA) genomes that typically contain two genes encoding for a replication initiator protein, called NS1, and the p ...
, and circovirus. Of particular concern are PERVs (porcine endogenous retroviruses), vertically transmitted viruses that embed in swine genomes. The risks with xenosis are twofold, as not only could the individual become infected, but a novel infection could initiate an epidemic in the human population. Because of this risk, the FDA has suggested any recipients of xenotransplants shall be closely monitored for the remainder of their life, and quarantined if they show signs of xenosis.[FDA. (2006]
Xenotransplantation Action Plan: FDA Approach to the Regulation of Xenotransplantation
Center for Biologics Evaluation and Research.
Pig cells have been engineered to inactivate all 62 PERVs in the genome using CRISPR Cas9 genome editing technology, and eliminated infection from the pig to human cells in culture.
Folklore
In the belief of traditional Irish fishermen, the pig is seen as a thing of bad luck and should not be mentioned.
Glossary of terms
Because the pig is a major domesticated animal, English has many terms unique to the species:
* ''barrow'' – a castrated male swine
* ''boar'' – a mature male swine; often a wild or feral
A feral () animal or plant is one that lives in the wild but is descended from domesticated individuals. As with an introduced species, the introduction of feral animals or plants to non-native regions may disrupt ecosystems and has, in some ...
swine
* '' boneen'' – a very young pig (Ireland)
* ''farrow'' (noun) – a litter of piglets
* ''farrow'' (verb) – to give birth to piglets
* ''gilt'' – a female pig that has never been pregnant or is pregnant for the first time
* ''hog'' – a domestic swine, especially a fully-grown specimen
* ''parcel'' – collective noun for pigs
* ''pig'' – strictly, an immature swine; more generally, any swine, especially of the domestic variety
* ''piglet'' – a very young pig
* ''queen'' – a female pig that has never been mated
* '' savaging'' – the act of a sow attacking her own piglets, sometimes killing and cannibalising them
* ''shoat'' – a young pig, especially one that has been weaned
* ''sounder'' – collective noun for pigs
* ''sow'' – a mature female swine
* ''swine'' (singular and plural) – hogs collectively or generally; also a derogatory epithet[ Dictionary of Agriculture (2006), "swine," 240. "''noun'' a collective term for pigs"]
* '' swineherd'' – one who tends to swine raised as livestock; a pig farmer
See also
* Farming
** '' Mycoplasma hyorhinis''
** Peccary
A peccary (also javelina or skunk pig) is a medium-sized, pig-like hoofed mammal of the family Tayassuidae (New World pigs). They are found throughout Central and South America, Trinidad in the Caribbean, and in the southwestern area of North ...
(domestication)
* List of individual pigs
This is a list of notable pigs.
General
Arnold
Arnold was the Ziffels' pet pig on the TV sitcom ''Green Acres''. He would perform anthropomorphic activities such as coming uninvited into the Douglas home, turning on the television and watching ...
* Pet
** Pigs in culture
** Truffle hog
A truffle hog is any domestic pig used for locating and extracting the fruit bodies of the fungi known as truffles from temperate forests in Europe and North America. Pigs have an exceptional sense of smell, and are able to identify truffles from ...
** Xenotransfusion
Xenotransfusion (from Greek '' xenos-'' ''strange'' or ''foreign''), a form of xenotransplantation, was initially defined as the transfer of blood from one species into the veins of another. In most cases, it is a transfer of blood between a non- ...
* List of pig breeds
There are hundreds of breeds of the domestic pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal ...
Footnotes
References
Animal Welfare AVMA Policy on Pregnant Sow Housing
*
CAST Scientific Assessment of the Welfare of Dry Sows kept in Individual Accommodations- March 2009
*
External links
An introduction to pig keeping
British Pig Association
Globe and Mail article Canada's transgenic Enviropig is stuck in a genetic modification poke
Information on Micro Pigs
gilt pig breeders
JSR Genetics
Pig genetics company
Pig Sanctuary
Swine Care
Swine Study Guide
from UC Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The institut ...
The process of pig slaughtery
{{DEFAULTSORT:Pig
Mammals described in 1777
Mammals as pets
Livestock
Pork
Taxa named by Johann Christian Polycarp Erxleben
Sus (genus)