Pig

I

Introduction

Pig, domesticated mammal of the swine family, extensively raised in almost every part of the world as a food animal. Pigs belong to the order of even-toed hoofed animals. They are further classified into the suborder of animals with 44 teeth, including two enlarged canines in each jaw that grow upward and outward to form tusks. The terms “pig”, “swine”, and “hog” are often used interchangeably for these animals.

Pigs are probably descended from two wild swine, one species from Europe and the other species from south-eastern Asia; they were perhaps first domesticated in China about 9,000 years ago, and later in Europe. They were introduced into the Americas by Christopher Columbus and the Spanish explorers.

II

Characteristics

An adult domestic pig has a heavy, rounded body; a comparatively long, flexible snout; short legs with cloven hooves; and a short tail. The thick but sensitive skin is partly covered with coarse bristles and exhibits a wide range of colour patterns. Like all swine, domestic pigs are quick-footed, intelligent animals.

Well adapted for the production of meat because they grow and mature rapidly, pigs have a short gestation period of about 114 days, and they produce large numbers of young (piglets) each time they give birth. They are omnivorous and can scavenge a wide range of foods—perhaps one of the reasons they were first domesticated. As food sources, they convert cereal grains and legumes, such as soya beans, into meat. Other than meat, products from pigs include leather (pigskin) for luggage, footwear, and gloves, and bristles for brushes. For centuries they have also been used as a primary source of edible fat. In Britain and many other countries pigs were bred for the production of lean meat and were called bacon-type pigs. In the United States, until the mid-1920s, they were also bred for the production of large amounts of lard. Modern swine are somewhere between these two types and are known as meat-type pigs. As the demand for fats has decreased, however, meat-type pigs have been developed to resemble the bacon-type more closely.

III

Breeds

The types of pigs that have been bred reflect their major use. An estimated 90 breeds are recognized today, in addition to more than 200 varieties.

Eight major breeds are raised in Western countries. The Berkshire (black with white points) and the Yorkshire (also called Large White) originated in England. The Chester White, Duroc (red), Hampshire (black with a white belt), Poland China (black with white points), and Spotted (black with white spots) originated in the United States. The Landrace, a large, long, white pig, came from Denmark. The major breeds also differ in growth rate, the number of young produced, mature body size, and ability to graze.

Most commercial pig production is based on cross-bred animals, because cross-breeding results in hybrid vigour. The most-used systems are two-breed and three-breed rotational crossing. In two-breed crossing, the boar (male) of one breed is bred to the sow (female) of another breed. The offspring of this cross is bred to a boar of the same breed as the sow in the first cross, and the offspring of this cross is then bred back to a boar of the same breed as the boar in the first cross.

IV

Production

Pigs are reared under more intensive conditions than cattle and sheep. Such enterprises fall into three broad groups: production of pure-bred breeding stock, production of feeder pigs, and growing and finishing of feeder pigs for sale and slaughter. Some producers carry out all three activities, and have built large farrowing units, where hundreds of sows can give birth.

Intensive production requires expert management and the cooperation of several different specialists, such as veterinary surgeons and nutritionists. Feed costs account for about 75 per cent of the total production expenses, so careful selection of feeds for their nutritional adequacy and economy is important. Many other important elements must also be controlled when pigs are raised under confined conditions. Newborn pigs are highly sensitive to cold. In addition, pigs have no sweat glands, so larger animals must have facilities for keeping cool in warm environments. Proper ventilation also removes toxic gases, primarily hydrogen and ammonia from waste products. In addition, because the animals are confined in intensive production units, they must each be allotted a given amount of space. This ranges from about 0.3 sq m (3 sq ft) for each young pig to approximately 1.4 sq m (15 sq ft) for breeding sows.

Under confinement, disease is held in check by vaccination, control of wildlife carriers of disease, antibiotics, and, in some cases, eradication of the disease-producing organisms. Compounds that can control the reproductive cycle, the length of the gestation period, and the timing of births have made it possible to control the breeding and farrowing so that a minimum of labour is required during weekends, when such labour is more expensive.