Pigs are mammals of the Artiodactyla order, also called "even-toed ungulates" (hoofed animals). They have four toes on each foot, with the two large middle toes being used for walking. They belong to the biological family Suidae, which includes both domestic pigs and their wild ancestors. Artiodactyla also includes peccaries, hippopotamuses, camels, chevrotains (mouse deer), deer, giraffes, pronghorn, antelopes, sheep, goats and cattle.
Pigs are omnivorous, which means they eat both animals and plants. Pigs have an excellent sense of smell. Their snout is a very sensitive organ and they use it to dig into the soil to find food.
Pigs do not have sweat glands, so they cool themselves using water or mud during hot weather. They also use mud as a form of sunscreen to protect their skin from sunburn. Mud also provides protection against flies and parasites. Pigs have a full set of 44 teeth. The canine teeth, called tusks, grow continuously and are sharpened by the lowers and uppers rubbing against each other.
Pigs are a social species and the females typically live in small groups of a few sows and their piglets. When sows give birth (called farrowing), they will seek a private area, returning to the group with their piglets when they are about a week old. Mature males live relatively solitary lives except during mating season when they will join groups of females. They may also occasionally form bachelor groups.
Their highly developed social behavior is evident soon after birth when piglets begin to form dominance hierarchies by competing for the best teat those closest to the sow's head and defend it. Piglets begin eating solid food at three weeks of age and are weaned between 13 - 17 weeks of age in nature. However, piglets on factory farms are weaned much earlier.
Pigs' natural tendency to mingle and remain in stable groups with conspecifics means the confinement and isolation of being constantly housed in sow stalls results in immense frustration and deprivation.
The behavior of domestic pigs closely resembles that of their wild ancestors. Foraging is a favorite activity, occupying them several hours a day. Pigs eat considerable amounts of high-fiber food including roots. Despite the stereotype that they are unclean animals, pigs select specific areas for defecating and urinating which are separate from their lying areas.
In addition to finding pleasure from rooting about in the straw or the ground for food, pigs enjoy rubbing their bodies against a hard surface and liked to be scratched and rubbed, particularly behind their ears, backs, sides and rump. They also enjoy lying huddled together to keep each other warm.
Pigs housed in barren pens such as those common to factory farms containing concrete flooring and no rooting material means pigs housed in these conditions are chronically stressed and bored.
Intelligence and Cognition
Cognition includes mental processes used to store, process, recall and use information. Studies demonstrate pigs to have highly developed cognitive skills and are capable of learning complex cognitive processes such as problem-solving requiring them to grasp rules, visual, spatial and olfactory discriminations, social learning and memory, and tasks that involved controlling their environment, such as adjusting lighting. One recent study published in the scientific journal Animal Behaviour and reported on in The New York Times found that pigs were capable of locating a food object hidden behind a solid barrier but visible to them in a mirror. Mirror image recognition is a very clear indication of some degree of self-awareness in animals. Pigs have even learned to play video games using a joy stick!
Pigs' high degree of intelligence is an important consideration both in terms of their welfare and the suffering they experience in barren, deprived environments. Their mental, emotional and social needs, like their physical ones, are important to their well being. The absence of stimulation inherent in intensive production systems causes pigs boredom and psychological distress leading to behavioral problems common in commercial agriculture systems like bar biting, tail biting, vacuum rooting or head bobbing.