Why study pig cognition? “The work of teaching and organising the others fell naturally upon the pigs, who were generally recognised as being the cleverest of the animals.” George Orwell, in Animal Farm, summarises a widely held suspicion that it is pigs that are the most astute, wily, and even devious, of our farm species. Look a pig in the eye and you may be forgiven for thinking that there is a person peering back at you from behind a mask. There is something about that human-looking eye, the alert, inquisitive, responsive behaviour, and the hairless body, that intrigues us and elicits a feeling of familiarity and even equality. Pigs are indeed physiologically similar to humans, but what about their cognitive abilities? Do pigs live up to Orwell's billing? These questions are of interest not only in order to establish the truth about popular portrayals of pig intelligence, but also because pigs are a major source of food. In 2008, the Food and Agricultural Organization estimates that there were some 941 million domestic pigs worldwide, kept in conditions ranging from outdoor pasture or woodland to intensive indoor farms where breeding sows live in metal crates that allow them to stand up and lie down, but do little else. Understanding pig cognition may tell us how different housing conditions impact on their mental state, and suggest management procedures that take account of their cognitive capacities in order to minimise stress and enhance welfare.

How do pigs behave in the wild? Common agricultural breeds such as the Landrace, rare breeds like the Gloucester Old Spot, and specially bred laboratory strains such as the Göttingen minipig are all domestic pigs descended from the Eurasian wild boar (Sus scrofa). The behaviour and social organisation of feral domestic pigs is much like that of the ancestral species. Pigs live in matrilineal family groups of two to five females with their young offspring and, during the breeding season, an adult male. Yearlings may continue to associate with the group but male offspring usually disperse to form ‘bachelor’ groups. Family groups forage together for food that is distributed patchily both in space and time. Given this social lifestyle, pigs would likely benefit from being able to discriminate between group mates and unfamiliar intruders, remember the location and attributes of food patches, use others as a source of information about where food is, and even conceal information about a food source from potential competitors. So, what do we actually know about these and other cognitive abilities in the domestic pig?

Can pigs tell each other apart? When unfamiliar pigs are mixed together (as happens regularly on pig farms), they fight vigorously, causing welfare and production problems. This behaviour likely reflects an evolved tendency to deter intruders from abruptly entering the family group, and indicates that pigs discriminate group-mates from non-group-mates. However, it does not tell us how sophisticated their discrimination abilities are. In recent research, pigs have been trained to discriminate between individuals for a food reward. They can do this even when they are unfamiliar with the individuals and the individuals themselves are litter-mates and hence presumably quite difficult to tell apart. Some pigs can discriminate even when only provided with cues in one sensory modality (smell, appearance, or sound).

Although these findings indicate that pigs can tell individuals apart, it remains to be discovered whether this ability reflects a cognitive concept of other individuals as distinct entities characterised by a cluster of physical and behavioural characteristics. It is also unclear how long pigs remember others for. According to some studies this could be three to six weeks or more, but these are based on observations of aggressive behaviour when previous group-mates are re-united, and such aggression may or may not occur for a variety of reasons, including re-establishing social order between recognised individuals, variation in the aggressive ‘personalities’ of individuals, and actual forgetting of another individual. Studies using specific measures of social recognition are needed to properly establish how long pigs remember others for.

Pigs in space… As their behaviour in the wild would predict, pigs have good spatial cognitive abilities. For example, in a spatial memory task involving twice daily visits to an arena containing several potential food sites, they rapidly learn to find where food is hidden during the first visit of the day, and to remember and return to the same location for more food on the second visit, some minutes or hours later. Whilst pigs readily learn to return to a site which they have recently depleted of food — a ‘win-stay’ strategy which is beneficial under captive conditions due to repeated provision of food at the same place — when given the opportunity they, like many species, show a preference for a ‘win-shift’ foraging strategy (avoiding sites where they have recently fed). This facilitates efficient searching, avoiding revisits. Pigs can also learn the locations of two sites containing different amounts of food, and preferentially return to the one of greater value.

Exploitative and deceptive pigs? Equipped with well-developed abilities for remembering where food patches are, pigs augment these by using group-mates as further sources of information about the location of food. This has been studied using a variant of the foraging arena task mentioned above, in which pigs forage in pairs ( Figure 1 Studying competitive foraging in the domestic pig. Show full caption Mendl and Nicol (2009) Mendl M.

Nicol C.J. Learning and cognition. Pigs are trained and tested daily in a foraging arena. (A) In the first trial of the day, a pig forages and finds the location of food for that day. (B) In the second trial of the day, the ‘informed’ pig is re-introduced into the arena with its companion who does not know where food is. Over repeated trials the behaviour of the two pigs changes as firstly the companion learns to follow the informed pig to the food, and then the informed pig develops behaviours which minimise the chances of the companion exploiting its knowledge. Adapted with permission from Equipped with well-developed abilities for remembering where food patches are, pigs augment these by using group-mates as further sources of information about the location of food. This has been studied using a variant of the foraging arena task mentioned above, in which pigs forage in pairs ( Figure 1 ). One ‘informed’ (I) pig knows the location of food (having searched the arena a few minutes previously), while its larger ‘non-informed’ (NI) companion simply knows that food is somewhere in the arena, but not where. Each pair of pigs forages together daily (each day the food is hidden at a randomly selected location). Initially the I pig goes straight to the food, while its NI companion searches locations systematically, and occasionally bumps into the I pig chomping away at the baited site. After some days, most NI pigs start to follow their pair-mates, having apparently learned that the I pig knows something they don't. NI pigs thus make use of their partner's knowledge and, because they are larger, exploit this knowledge by displacing them from the food.

After more days of this foraging arms-race, many of the I pigs develop behaviours that might allow them to overcome exploitation. They tend to turn towards or actually go to the baited site only when their NI pair-mate is either some distance away, moving away from the food, or out of sight (behind a barrier). I pigs also suppress their preference for first visiting the larger of two food sources when they are with an exploiting companion. Interestingly, they don't do this when with a non-exploiting companion, further indicating quite subtle social discrimination abilities. The I pigs' apparently deceptive behaviour is similar to that observed in chimpanzees, Mangabey monkeys and ravens. Maybe they intend to deceive their companion, understanding their exploitative intentions and how to overcome them; pigs might indeed be as devious as Orwell painted them. Another explanation, however, is that I pigs learn that if they visit the baited site when the NI pig is in view, coming towards them, or close by, they will usually be unceremoniously barged out of the way. They therefore suppress movements towards the food in these circumstances. The resulting behaviour appears deceptive, but it is the result of associative learning, rather than so-called ‘higher level’ understanding of the intentions of others. Unfortunately, these studies don't yet allow us to conclude which explanation is the correct one.

Really clever pigs? So, pigs can show sophisticated social behaviour, but is there any evidence of a truly powerful primate, corvid, cetacean or elephantine-like mind behind this? Recent findings are intriguing. Pigs with experience of a mirror move away from the reflection of a food bowl and around a barrier to get to the bowl, rather than looking behind the mirror as mirror-naive subjects do. This indicates that they can learn about the visio-spatial properties of mirrors and use them to guide their behaviour in appropriate ways. No tests of mirror self-recognition, used to assess the possibility that animals have a self-concept, have been carried out, but there is clearly potential for such studies. Having a self-concept is thought to be a pre-requisite for a ‘theory of mind’ — the understanding that other individuals have mental states and knowledge like oneself. The ability to take the visual perspective of others may be one indicator of theory of mind.

In a tightly-controlled study, one out of 10 pigs showed behaviour consistent with understanding that one of its companions had witnessed the location of a food-baiting event and hence knew where food was, while its other companion who, like itself, was shielded from the food-baiting event by an opaque barrier, had no such knowledge. Most of the other pigs refused to follow either potential informant, and, although one success out of ten is perhaps not convincing and there are alternative, if tortuous, explanations, it remains possible that the single pig genuinely demonstrated visual perspective taking. Another ability thought, until recently, to be uniquely human is the capacity for episodic memory — remembering what happened where and when. A recent study suggests that minipigs may be able to remember what object was encountered where, and in which context, indicating possible episodic-like memory in this species.

What implications do studies of pig cognition have for an understanding of their welfare? The relationship between cognitive ability and the potential for suffering is not straightforward. For example, if pigs do have episodic memory and future planning abilities, this will help them to predict potential challenges and plan appropriate action, but also render them vulnerable to anxiety about the future, and memory of unpleasant events. More fundamentally, it is unclear how the capacity for conscious suffering is related to cognitive (information processing) ability. Although species with a self concept may be self conscious, allowing them to experience “I feel pain”, suffering may be just as great in species that possess only phenomenal or feelings consciousness — conscious awareness of basic emotions and sensations — and experience “this is painful”. It is not obvious why phenomenal consciousness, the key attribute that enables suffering and hence poor welfare, should be restricted to species capable of complex cognitive feats.

If we assume that pigs possess phenomenal consciousness, studies of cognition can help us identify situations in which they may suffer, and management procedures that minimise these. For example, pigs can learn associations between visual cues and the duration of a subsequent period of confinement. These time-perception abilities could be utilised by signalling the duration of upcoming husbandry procedures, hence increasing their predictability and reducing their aversiveness. Our understanding of the social skills of pigs suggests that, given the opportunity, they can resolve conflicts in subtle ways rather than by damaging fights. Preliminary studies indicate that, when pigs are given time to assess each other through a barrier prior to being mixed, this does indeed reduce subsequent aggression.

Whilst our understanding of pig cognition is at an early stage, the complexity of pig behaviour is already evident, indicating sophisticated associative learning abilities and, although more evidence is needed, perhaps the capacity for episodic memory, intentional deception and even theory of mind. Even if these latter abilities are not present, it seems unlikely that pigs will be fulfilled by a life spent standing up and lying down in a metal crate. One way forward may be the use of ‘cognitive enrichment’ to enhance quality of life, and it is encouraging that providing pigs with cognitive tasks has recently been shown to reduce abnormal behaviour, decrease fearfulness, speed up wound healing, and even alter gene expression in reward-sensitive opioidergic systems in the brain. Allowing pigs to use their cognitive talents appears to be an important way of enhancing their welfare.