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Pigs were first domesticated in the Near East around 8500 BC and subsequently brought to Europe by agriculturalists. Soon thereafter, agriculturalists are thought to have incorporated local wild boars into their domesticated pig herds.

The domestic pigs of today maintain many of the natural characteristics and behaviours of their forest dwelling wild ancestors. Wild boar spend much of their day foraging and rooting for food; they use trees to shade them from the sun and shelter them from the rain and wind. The modern day pig, as descendants of forest individuals, also have special snouts which help them to dig in the soil for food and naturally need soft substrate to allow them to perform their natural foraging behaviours.

Wild pigs are often maligned as ecosystem destroyers, but in certain habitats their actions in fact encourage biodiversity. The nesting practises of native pigs in Malaysian rainforests are critical to maintaining diverse and balanced tree communities. Prior to giving birth, pigs build birthing nests made up of hundreds of tree seedlings, usually on flat, dry sites in the forest. As they build their nests, the pigs kill many of the dominant seedlings and inadvertently reduce the abundance of locally dominant tree species, to the benefit of rarer local species, supporting tree diversity.

Both wild and domesticated pigs love to wallow in the mud. As well as being a fun thing to do, pigs do this to keep cool, and protect themselves from insect bites and the sun.

Pigs also like to keep clean and do not like to wallow in their own mess, if pigs are penned in they will use a corner of their nest as a toilet to ensure they keep the rest of their nest clean.

Pigs are very social animals, and are happiest when they are living within a group of pigs. They live in matrilineal family groups of two to five females and their young offspring. They form close friendships, and show a preference to spend time foraging, and sleeping with these friends, staying close together and synchronising their activities.

They establish stable social groups, with each individual pig being able to recognise others within their herd and to understand their relative social status, and they are known to be less stressed when they are with a friend.

Each pig has its own personality and has behavioural traits that reflect their complex personality type, this is particularly important in group living animals that need to learn to get along with individuals that may have differing personalities to themselves.

Pigs’ personalities, combined with their moods, affect how they make decisions. Proactive pigs are more likely to be optimistic, and reactive pigs are more likely to be pessimistic when it comes to decision making.

Some pigs are even known to be ‘peace-keepers’. Due to domestic pigs often being housed in close proximity, conflicts arise and in some cases a bystander pig may intervene in a fight to reduce the number of attacks by the aggressor or to help reduce the anxiety of the victim.

Pigs are thus sensitive and complex animals who experience a wide range of emotions expressed through behaviour, vocalisations, facial expressions, ear and tail movement,and chemically, through scent. Pigs experience emotion physiologically through increased heart rate, altered hormone levels, and changes in body temperature. They can be anxious, stressed, happy and content and demonstrate both optimistic and pessimistic outlooks depending upon their individual situation.

They use a variety of sophisticated communication techniques which have evolved over millions of years to help them to share information with each other and protect each other from harm. They communicate vocally via a wide variety of oinks, grunts, and squeals for different situations, from wooing their mates to expressing hunger, each different sound conveying meaning to other pigs within their social network, and this being individually understood and acted upon.

They communicate their emotions in their grunts, with individuals experiencing positive emotions known to have shorter grunts with a lower frequency and less noise than pigs experiencing negative emotions.

Piglets express emotional distress by screaming when they are physically separated from their mothers but in visual contact, and grunting when they are completely isolated.

Our understanding of the meaning within the pigs vocal communication is also vitally important with regards to understanding their welfare expressed through either positive or negative emotional states by pigs on farms and acting upon this information to improve the lives of farmed pigs.

Pigs also express their emotions visually, pigs who are playing, and likely feeling positive emotions, wag their tails whereas pigs who experience negative emotions are likely to move their ears more.

Pigs also communicate through scent, a pig's sense of smell develops early in their life and is very important for their survival as they need to follow chemical cues, such as the odour of their mother allowing them to smell their way back to the safety of her protection if needed.

Pigs release pheromones in their saliva, urine and facial glands. Passing on important information to let others know where they have been and to encourage others to follow. These odours are also used for individual recognition and pigs who are unable to see are able to recognize other individuals in their group by scent, indicating the strength of these senses.

Pigs understand each other, knowing when another pig is feeling happy or stressed and understanding the emotional states of other pigs within their herd. They pass on their emotions to other pigs, with pigs being able to spread their good or bad mood to others within their group via emotional contagion, and they empathise with each others emotional state

Pigs are also great mums, protecting their youngsters from harm and keeping them secure. They even build a nest of straw and hay for their piglets to ensure they are comfortable and warm. New-born piglets quickly learn to run to their mums’ voices when she calls, and mums ‘sing’ to their young whilst they are nursing, providing them with a comforting environment and keeping her piglets calm and relaxed as they feed. Mum also memorises the call of her piglets, and responds to their needs when they call for her.

Play is a very important part of development for piglets and they love to play socially, play fighting and chasing after one another. Pigs engage in complex play both with other pigs and with objects. If given the opportunity, pigs will play with all sorts of objects, from balls to sticks. They will carry, throw and shake objects in bouts of play, and pigs will even repeatedly use slides.

In addition to being socially and emotionally complex, pigs are also cognitively complex individuals.

Pigs are capable of learning from each other socially, copying the complex behaviour of another pig and understanding their objectives and intentions.

They have excellent memories, being able to individually recognise over 30 other pigs within a herd, and they can remember these individuals for many years even if they have not seen them for a long period of time.

Pigs can also remember solutions to complex problems many months after they have learnt such solutions such as how to perform certain actions to receive food rewards.

Pigs have good spatial memories returning to feeding sites that have provided them with access to food previously and if provided with food at two sites containing different amounts of food will preferentially return to the one of greater value, demonstrating an ability to discriminate between food quantities and memorise the fact that one location provides more food than another. Pigs also show some impulse control by waiting for food they like the most, rather than just taking what’s immediately available.

Pigs have episodic memory abilities, remembering specific details (what, where, and when) of events after hours, weeks, and even years have passed.

Pigs are visual discriminators, being able to recognise people based on their body size and facial characteristics, and they can identify and recognize the likeness and differences in people’s faces and the capacity to remember these differences. Pigs not only discriminate between front and back views of human heads, they use certain facial features such as our eyes or mouth as cues.

Piglets learn to avoid or approach individual humans depending on their past experiences with them, remembering an aversive handler for weeks after having a negative experience, and pigs are capable of understanding the intention of humans, and have passed the “pointing test,” meaning that they can locate a food reward using the cue of a person.

Pigs can understand the concept of reflections in a mirror, being able to locate food bowls reflected in mirrors with an understanding of the visio-spatial properties of mirrors and using them to guide their behaviour in appropriate ways.

Pigs are also problem solvers with remarkable levels of behavioural and mental flexibility. They can learn how to solve complex problems such as how to find hidden food items and they remember how they solve these problems to help them again in the future. They can identify and fetch objects upon request, they can understand commands which involve an action i.e. ‘push a dumbbell onto the mat’ and make comparisons of objects based on colour, odour or location. Pigs can also do this with no instruction by being told ’figure out what you are supposed to do’.

They are also capable of learning to perform tasks they have not evolved to master such as how to use a joystick to move objects on a computer screen. When they move the object into the desired position they receive a reward. Indicating they understood that the movement of the joystick was connected to the cursor on the computer screen. Pigs learn to do this as quickly as chimpanzees, demonstrating advanced cognitive ability.

Wild boars have been observed using water as a tool, taking pieces of apple to a stream to wash off the dirt before eating them, and Visayan warty pigs have been observed digging by using a piece of bark held in the mouth to help to dig a nest for their piglets. Wild Visayan warty pigs have also been observed pushing rocks toward an electric fence to test if it is producing an electric charge or not.

Pigs are also capable of assessing by observation what information another pig knows in relation to them with regards to how to perform a task with a reward. They can then choose to follow the individual with more information than themselves to receive the same reward.

Pigs are socially, emotionally and cognitively complex animals.

There are an estimated 1.3 billion pigs raised for consumption every year. Many within highly restrictive confinement especially for the females, kept in intensive crates prior to giving birth. Due to their close proximity and crowded living conditions piglets are likely to have their teeth clipped to minimise biting injuries and males are castrated often with no pain relief.

For intensively reared pigs their housing conditions are likely to become very unhealthy and this promotes the replication of viral and bacterial infections.

We have benefitted immensely from our relationship with pigs. We owe them respect and must do all we can to ensure the suffering of these smart and sensitive animals comes to an end and we can live in harmony with individuals that wish to bond with and protect those they care for.

Written by Dave Neale, Animal Welfare Director, Animals Asia Foundation

Latest update 10/02/2023

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