pig iron: see iron.

pig: see swine.

guinea pig, domesticated form of the cavy, Cavia porcellus, a South American rodent. It is unrelated to the pig; the name may refer to its shrill squeal. Guinea pigs were raised by the Incas and have long been used as food in South America. They were first imported into Europe from Guiana in the 16th cent. There are a number of varieties, some with short, smooth hair and others with longer hair, and a great range of color combinations, including mixtures of black and white and many shades of brown. They have rounded bodies, large heads, and blunt noses and reach a length of 6 to 10 in. (15-25 cm) and a weight of 1 to 2 lb (450-900 grams). Females produce three to five litters, usually of three or four young, per year. The guinea pig's rapid reproductive rate and high resistance to disease make it a valuable laboratory animal; it is used for testing serums and antitoxins and for experiments in genetics and nutrition. It is also sometimes kept as a pet. It is classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Caviidae.

earth pig: see aardvark.

or wild boar or wild pig

Any wild member of the pig species Sus scrofa; the ancestor of domestic pigs. It is native to forests ranging from western and northern Europe and North Africa to India, the Andaman Islands, and China and has been introduced to New Zealand and the U.S. It has a bristly, blackish or brown coat and stands up to 35 in. (90 cm) tall at the shoulder. Except for old, solitary males, boars live in groups. They are omnivores and are good swimmers. They have sharp tusks and, though normally not aggressive, can be dangerous. Because of its strength, speed, and ferocity, the boar has long been a prized game animal.

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Heavy-bodied, solitary, slow-moving, nocturnal rodent with quills (modified hairs) along the back, tail, and, on certain crested species, the neck and shoulders. The quills are easily detached when touched. The New World species (four genera in family Erethizontidae) are arboreal and have barbed quills; the Old World species (four genera in family Hystricidae) are terrestrial and have unbarbed quills. The North American porcupine (Erethizon dorsatum), about 31 in. (80 cm) long with a tail about 12 in. (30 cm) long and quills about 3 in. (8 cm) long, drives its powerful tail against an assailant. For food, it favours the tender tissue beneath tree bark. Crested porcupines, the typical Old World porcupines, run backward, quills erect, into the enemy. They eat roots, fruit, and other vegetation. The African crested porcupine, the largest terrestrial rodent in Europe and Africa, may weigh 60 lb (27 kg) and have quills 14 in. (35 cm) long.

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Any wild or domestic even-toed ungulate (family Suidae) that is a stout-bodied, short-legged omnivore, with thick, sparsely bristled skin, a long mobile snout, small tail, and hooves with two functional and two nonfunctional digits. Pigs are native to European, Asian, and North African forests. Wild pigs use their tusklike teeth to forage and for defense; the teeth of domestic pigs, which were developed from wild pigs in Europe circa 1500 BC, are less developed. Pigs are regarded as highly intelligent. Domestic pigs are classified as lard (thick fat, carcass weighing at least 220 lbs, or 100 kg), bacon (carcass about 150 lbs, or 70 kg), and pork (carcass about 100 lbs, or 45 kg) pigs, depending on the principal product derived from them; they are also a source of leather. Today they are usually bred in almost complete confinement. Seealso boar, hog.

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Domesticated species (Cavia porcellus) of South American cavy (family Caviidae). It resembles most other cavies in being stout, short-legged, and about 10 in. (25 cm) long. It has small ears, no external tail, and a coat that is black, tan, cream-coloured, brown, white, or a combination of these colours. Hair length and texture vary among varieties. It feeds largely on grass and other green plants. Domesticated in pre-Incan times, it was introduced into Europe in the early 16th century. It is a popular pet and a valuable research animal.

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