Pigs

Pigs, hogs, or swine consist of about eight species of mammals in the family Suidae, which is part of the order Artiodactyla, the cloven-hoofed ungulates . Pigs are closely related to the peccaries (family Tayassuidae) and hippopotamuses (family Hippopotamidae). The natural distribution of pigs includes Africa , Europe , and Asia , but one species, the domestic pig (Sus scrofa), is now found almost worldwide as a domestic and feral species.

Pigs have a relatively large head, with a long, cone-shaped snout, small eyes, long ears, a short neck, short legs, and a stout body. The skin of pigs is thick and tough, and it may be sparsely or thickly haired, depending on species. The largest pigs can weigh more than 660 lb (300 kg).

Pigs have a flat-fronted, cartilaginous, malleable, almost hairless nose that is very tactile, and along with the extremely keen sense of smell , helps these animals to find and root out their food, which is often buried underground. Pigs also have an excellent sense of hearing , which is very useful in helping them to detect the activities of potential predators. However, pigs have poor vision , and they can only see effectively over short distances. The canine teeth of pigs grow continuously, and in male animals (or boars) these can be very large, and curl as tusks outside of the mouth. These sharp teeth can be used by mature pigs as slashing weapons, either in defense against a predator , or in combat between male pigs during the breeding season.

Pigs are omnivorous animals, eating a highly varied diet. Most of the foods consumed by pigs are plant tissues, especially underground roots, rhizomes, and tubers, which are excavated using the snout. Pigs also eat the foliage of many plants, as well as nuts, seeds , and fruits that may be found on the ground. Pigs are opportunistic predators, and will eagerly eat birds eggs and nestlings if these are discovered, as well as small rodents , snakes , and other prey . Pigs will also attack larger, disabled animals, and will eat carrion.

Pigs occur in a wide range of habitats, from alpine tundra , through most types of temperate and tropical forests , savannas, swamps, and the vicinity of human settlements. Wet places are a necessary component of all pig habitats, because mud bathing is important to the physical and mental health of these animals.

Most species of pigs are social, with the animals generally living in family groups consisting of at least a mature female (or sow) and her young. Mature boars are generally solitary, except during the mating season. Grunting and squeaking noises are important in the communications among pigs. Baby pigs are precocious, and can move about only a few hours after their birth . Broods of pigs can be quite large, and can exceed a dozen piglets. Young pigs often fall victim to predators, but mature animals can be ferocious in their self-defense, and are not an easy mark as prey. Pigs can live to be as old as 25 years.

Species of pigs

The true pigs include four species in the genus Sus. The wild boar (Sus scrofa) is the progenitor of the domestic pig. This species is native to the temperate regions of Europe, North Africa, and temperate and tropical Asia. The wild boar has been introduced far beyond its original range, and now occurs widely in parts of North America , New Guinea, Australia , New Zealand, and many other islands of the Pacific Ocean.

Wild boars can reach a weight of up to 770 lb (350 kg). The curved, sharp tusks of large boars can reach a length of 9 in (23 cm). These formidable tusks are used as slashing weapons, and for cutting and digging up food. Wild boars live in social groups, commonly consisting of one or several mature females and their offspring, which can total as many as 12 in a single litter, although the usual number is smaller. Mature male animals tend to live by themselves, except during the breeding season.

Wild boars live in an extremely varied range of habitats, from dry prairies and savannas to wet swamps, and from lowland near sea level to montane and alpine ecosystems as much as 13,120 ft (4,000 m) in elevation. In addition, wild boars will eat an amazingly wide range of foods. Wild boars are primarily vegetarian, feeding on fruits, nuts, seeds, tubers, and rhizomes, with the relative importance of these in the diet varying geographically and with seasonal availability. However, wild boars will also opportunistically avail themselves of any animal foods that present themselves, including animals that are found dead as carrion, as well as those that can be easily predated, such as the eggs or nestlings of ground-nesting birds, or slow-moving rodents, frogs , or reptiles . Other than humans, wild boars may be more omnivorous than any other animal.

The bearded pig (Sus barbatus) occurs in tropical rainforests and mangrove forests of Malaysia and the Sunda Islands of Indonesia. This species can achieve a weight of up to 330 lb (150 kg), and it develops a beard of long hairs on its cheeks. Bearded pigs live in family groups or larger herds, which roam through the jungle looking for fallen fruits and other foods. Bearded pigs are relatively sedentary in most parts of their range, but in northeastern Borneo they undertake seasonal migrations in large numbers. Because these movements involve routes that are traditionally used, and are known to human hunters, these bearded pigs can be easily killed in large numbers during their migration .

The Javan pig (Sus verrucosus) occurs in grasslands , forests, and swamps on the islands of Java and Sulawesi in Indonesia, and also in some of the Philippine islands. Javan pigs can weigh as much as 330 lb (150 kg). The pygmy hog (Sus salvanius) occurs in forests of the southern Himalayas, particularly Nepal. This is a very rare species of pig, and can achieve a weight of about 440 lb (200 kg).

The bush pigs (Potamochoerus porcus) occur in tropical-forest habitats throughout sub-Saharan Africa and on Madagascar. Boars of these species have well developed and sharp canine teeth. These animals generally forage in small groups at dusk or during the night.

The warthog (Phacochoerus aethiopicus) is a barrel-shaped animal of the extensive savannas and open forests of central and southern Africa. The warthog has a big head decorated with large skin warts, and huge, outcurving tusks, which can be as long as 26.8 in (68 cm), but are more usually about 11.8 in (30 cm). Warthogs feed most actively during the day.

The giant forest hog (Hylochoerus meinertzhageni) is a rare species that occurs in tropical rain-forests of central Africa. Although the giant forest hog is a large animal, weighing as much as 297 lb (135 kg), it is shy and lives deep in relatively inaccessible habitats, and was not known to science until 1904.

The babirusa (Babyrousa babyrussa) is a strange-looking, almost hairless pig of swampy jungles and reedy thickets of Sulawesi and nearby islands in Indonesia. This species grows as large as 220 lb (100 kg). Some old boars can grow enormous, curling, upper tusks as long as 16.9 in (43 cm), that can develop as a complete, 360-degree circle . The upper canines of babirusa boars actually curl and grow upwards, and penetrate right through the skin of the upper jaw, so the head is actually protected by four, curling tusks, two on each side.

The domestic pig

The many distinctive races of domestic pig are all derived from the wild boar, and are sometimes designated as their own subspecies, Sus scrofa domesticus. The domestic pig is mostly raised as food for humans, and today a population of about 0.85-billion pigs are being raised in agriculture around the world.

Pigs are an ancient domesticate, and they have been cultivated by people for many thousands of years. Today, pigs are raised using various systems of husbandry, which vary enormously in their intensity. The oldest and simplest systems depend on locally free-ranging pigs, which return to their designated domiciles in the village each evening. Whenever they are needed for food or to sell as a cash-crop, individual pigs are killed or taken to the market, while the breeding nucleus is still conserved. Raising pigs in this relatively simple way is common in many subsistence agricultural systems in poorer parts of the world. For example, in the highlands of New Guinea pigs have long been an important agricultural crop, as well as being very prominent in the culture of the indigenous peoples, who measure their wealth in terms of the numbers of pigs owned by a person or village.

Of course, modern industrial agriculture involves much more intensive management of pigs than is practiced in these sorts of subsistence systems. Pigs raised on factory farms may be bred with close attention to carefully designed breeding lineages, often using artificial insemination to control the stud line. Industrial piggeries keep their animals indoors, under quite crowded conditions, while feeding the pigs a carefully monitored diet that is designed to optimize the growth rates. Fecal materials and urine represent a substantial disposal problem on factory farms, which may be resolved by disposal onto fields or into a nearby water body, or if this is prohibited, by building a sewage treatment facility. Pigs grown under these types of rather unsanitary, crowded conditions are susceptible to diseases and infections. Therefore, close attention must be paid to the health of the animals, and regular inoculations and treatments with antibiotics may be required.

The intensively managed husbandry systems by which pigs and other livestock are raised in industrial agriculture are often criticized by environmentalists and ethicists. The environmentalists tend to focus on the ecological damages associated with various agricultural activities, for example, the disposal of sewage and other wastes. The ethicists complain about the morality of forcing intelligent animals such as pigs to live under highly unnatural conditions. The life of an industrial pig includes living under conditions lacking in many sensory stimuli, exercise , and numerous other elements of a happy life, eventually to be crowded into trucks and trains to be transported to a central abattoir, where the animal is slaughtered and processed under generally brutal conditions. The environmental and ethical dimensions of modern animal husbandry are becoming increasingly important considerations in the ongoing debate about the relationships of humans with other species, and to ecosystems more generally. These are important issues in terms of the sustainability of our resource-use systems.

Domestic pigs are sometimes used in southern France to hunt for truffles, which are extremely flavorful and valuable mushrooms that are prized by gourmet cooks. The truffles develop beneath the ground, but they can be easily detected by specially trained pigs, thanks to their relatively high intelligence and extremely sensitive sense of smell.

Sometimes, individuals of the smaller races of pigs are kept as housepets. Pigs are highly social animals, and if raised from a young age they will become highly affectionate and loyal to humans. Pigs are quite intelligent animals, similar in this respect to the domestic dog (Canis familiaris), and this characteristic also enhances their qualities as a pet. In addition, pigs can be rather easily toilet trained. One of the most favored races of pig as pets is the Vietnamese pot-bellied pig.

Resources

books

Grzimek, B., ed. Grzimek's Encyclopedia of Mammals. London: McGraw Hill, 1990.

Nowak, R.M., ed. Walker's Mammals of the World. 5th ed. Baltimore: Johns Hopkins University Press, 1991.

Porter, V. Pigs: A Handbook to the Breeds of the World. Pica Press, 1993.

Wilson, D.E., and D. Reeder. Mammal Species of the World. 2nd ed. Washington, DC, Smithsonian Institution Press, 1993.

Bill Freedman

KEY TERMS

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Feral

—This refers to domesticated animals that have escaped to natural habitats beyond their natural range, and can maintain wild populations, as is the case of many introductions of wild boars.

Husbandry

—The science of propagating and raising domestic animals, especially in agriculture.

Omnivore

—An animal that eats a very wide range of foods, including plant materials, as well as animals. The animal foods may be either predated, or scavenged as carrion.