Pigs are one of the most common farm animals in the world. They are so familiar that we rarely consider the important, basic questions - what are they; where do they come from; why do we keep them? This section provides some answers which will help you better understand the unique characters of pigs and the roles which they serve.
1.1.1 WHAT IS A PIG?
Almost everyone can identify a pig. If we were taken to a farm and asked to point at a pig, most of us would have no hesitation in choosing the right animal. It is easy. There is a certain combination of shape, size, appearance, movement, smell and sound which tells us, unmistakably, that we are looking at a pig.
However, the pigs we see on farms are animals which have been shaped by hundreds - even thousands - of years of domestication and selective breeding. People first domesticated wild pigs and then gradually bred them into a huge variety of shapes, sizes and colors. Animals were selected for a number of purposes (discussed later) and to fit within a very wide range of physical environments. The "modern" pig we see today on commercial farms represents the current end-point of innumerable formal and informal selection processes. The "modern" pig does not exist in the wild but, obviously, carries genes derived from its original wild ancestors. And, sometimes, the process can run the other way.
This section answers the question, "What is a pig?", in two ways. First we look from the zoologist's perspective, placing the pig within mammalian taxonomy. Then we divert to an important related question, "Why do people raise pigs?".
This leads to the final part and the second answer to our original question, "What is a pig?". It examines the question from the farmer's perspective, "What does a pig represent to a farmer?"
1.1.2 THE ZOOLOGIST'S PERSPECTIVE
All known living organisms (and a large number of extinct ones) have been classified by taxonomists. The classifications use a hierarchical system. There are three primary classifications - Animals; Plants; Bacteria and Algae. All animals are included in the first broad general grouping (the Animal Kingdom), then classed into successively smaller and smaller sets of sub-groups. Within each stage of classification, animals with more similar characteristics are grouped together and the differences between each group become more pronounced. The general hierarchy of the classification is shown below. The names of the groups at each level from which the "modern" farm pig has been derived are shown in the right-hand column:
All animals are members of the Kingdom Animalia (also called Metazoa). All mammals belong to the phylum Chordata, sub-phylum Vertebrata (i.e., has a backbone) which includes fishes, reptiles, amphibians, birds and mammals. Pigs are in the class Mammalia, infra-class utheria (placental mammals). All mammals share three characteristics not found in other animals:
Three middle-ear bones.
The production of milk by modified sweat glands called mammary glands.
Pigs belong to the Order Artiodactyla (even-toed ungulates), Suborder Suina. The name ungulate refers to hoofed mammals which are superficially similar but not necessarily closely related taxonomically. Ungulates belong to the old order Ungulata, which is now divided into the orders Perissodactyla (odd-toed ungulates - including horses, zebras and rhinoceroses) and Artiodactyla (even-toed ungulates including antelopes, camels, cows, deer, goats, pigs, and sheep).
The living Suina or swine comprise the pigs, peccaries and hippopotamuses. Pigs belong to the Family Suidae. The suids or pigs are unknown in the Americas but well represented in the Old World continents (Africa, Asia, Europe). However, humans have introduced Sus scrofa, from which the domestic pig is derived, to many places around the world where they previously did not occur, including north America, New Guinea, Australia and New Zealand. The family of Suidae comprises three subfamilies and five genera:
The babirussa (Babyrousa), forest hog (Hylochoerus) and wild boar (Sus) are tropical and temperate forest forms of the pig. The water hog or bush pig (Potamochoerus) is semi-aquatic. The warthog (Phacochoerus) is a savannah woodland form.
The pig is an omnivorous even-toed mammal having incisors in the upper and lower jaws and prominent canines. They are not true ruminants, having a simple stomach chamber and molar teeth which are bunodont with rounded cusps. These types of teeth indicates they have broad diets consisting of many different kinds of foods with different consistencies. The canines form tusks which are used for defense and intra-specific aggression. They have four toes on each foot, but the outer ones are short and non-functional.
Typically, pigs are stocky, medium-sized animals with a barrel-like body. Head and body length is approximately 500-1,900 mm, tail length is about 35-450 mm, and adult weight can be as much as 350 kg. The thick skin is usually sparsely covered with coarse bristles or bristly hairs, but some suids are almost naked. The young are striped for camouflage except in Babyrousa and domestic Sus scrofa. The females of most genera have three or six pairs of mammae, but there is only one pair in Babyrousa. Suids have a two-chambered, simple, non-ruminating stomach.
The eyes are usually small and located high on the skull. Ears are relatively long and pointed, with a tassel of hairs near the tip. The skull is usually long and has a flat dorsal profile. One of the most notable characteristics of suids is the mobile snout, which has a cartilaginous disk at its tip and terminal nostrils. It is supported by a prenasal bone located below the nasals. The skull has a prominent occipital crest that is formed from the supraoccipital and parietal bones. The metapodials are not fused, and the first digit is missing from both forefeet and hind feet. All four digits have hooves, but these are only functional in locomotion on the middle digits (the third and fourth), as the smaller lateral digits are located higher on the limb (paraxonic).
The dental formula varies among the genera; a general formula for the family is: 1-3/3, 1/1, 2-4/2 or 4, 3/3 = 34-44. The upper incisors decrease in size laterally; the lower incisors are long, narrow and set at a low angle in the jaw so that they are almost horizontal. The upper canines grow out and backward into large, curved tusks; wear between the upper and lower canines produces sharp edges. The upper canines are ever-growing. The molars are bunodont or cuspidate.
Pigs are gregarious species and generally live in forests and woodlands. They shelter in tall grasses or reed beds and in burrows that are self-excavated or have been abandoned by other animals. Pigs are surefooted, fast runners and good swimmers. They are fond of mud baths. They are active mainly at night (nocturnal). Pigs are omnivores, and the diet includes fungi, leaves, roots, bulbs, tubers, fruit, snails, earthworms, small vertebrates, eggs and carrion. They use their muscular, mobile snout and
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