The Intelligence of Pigs

Some readers may be surprised to find the intelligence of pigs saluted in a November 10, 2009, New York Times column by Natalie Angier. She based her work largely on a new paper (Broom, Sena & Moynihan) in the Anglo-American journal, Animal Behaviour (note the British spelling) and her column  is an example of a well-researched popularization that all of us  (myself included)  should try   to emulate for both accuracy and interest.

The key finding is that pigs who are exposed to mirrors for as few as five hours prior to a subsequent test, learn the concept that mirrors are not windows, showing the pig another pig behind a pane of glass, but rather are reflections of themselves, and of their surroundings.

The key test in the study was the placement of a bowl of food in a location in a maze-like room with compartments. This prize  was reflected in a mirror that was at the end of a straight corridor within the maze, but the bowl itself was not actually in the straight path ahead, but rather off at an angle that could not be seen directly, only through viewing the mirror. Absent the mirror, there was no visual evidence of food.

All but one of the pigs who had prior mirror exposure rather quickly figured out that one did not go behind the mirror, to  find the bowl of food, but rather they proceeded  in the direction indicated by their understanding of  from where the reflection was coming.

The potential confounding factor of the pig following the scent of the food was handled by having the ambient air circulate rather vigorously throughout the room using a fan, spreading the tell-tale aroma around as evenly as possible.

One pig, was, well, a bit slow, and did not ever seem to get the hang of it.

Nature vs. Nurture in Pig Intelligence & Teat Ownership

In the genetics vs. nurture controversy on intelligence in the animal kingdom, there is evidence for both sides as being influential among pigs. Certain breeds are demonstrably more intelligent than others. Duroc breed pigs, for example, have unambiguously tested  smarter than Hampshires, and the consensus belief in the swine community  is that breed  is predictive of half of the individual differences among pigs in unrelated  intelligence.

The other half has to do with nutrition. Pigs that establish “ownership” of a particular nipple on a sow, often have a significant advantage in weight gain, over those who lose out in the initial milk allotment, even if those denied piglets ultimately get subsequent access to a nipple, and can feed afterwards. Tests of  identically  aged piglets, show that those that weighed  more tested better in more complicated mazes, a standard measure used in many animal intelligence tests.

More recent studies indicate that the presence or greater concentration of sialic acid in the sow’s  milk is strongly related to the development of the pig brain, and the teat-owning piglet  apparently gets more milk or perhaps more concentrated sialic acid. 

Learning &  Socialization

Pigs have a highly developed social structure and their young   clearly learn primarily from their sow mother first, and then from age-matching piglets. In Europe where many pigs have been released to the wild in order to regenerate and sustain wild boar populations -----they interbreed readily ----- the death of a sow even when the piglets are past weaning presents problems, because the sow teaches more than just simple foraging. They teach a measure of cooperation, and family bonding.

Tests show that pigs in captivity can detect which are their littermates just by looking, in the equivalent of a small police lineup, even after separation and the masking of any telltale scents,  or communicating calls or sounds. In other words, they retain a visual memory of their family group. Their recall  can be reinforced with food rewards to optimize performance in some measures of litter mate identification, such as speed of recognition. In other words,  pigs can sharpen their native memory through focus on task they eventually recognize as being rewarding. They are quite educable on the whole.

Tests also show that pigs remember where food is stored, even if hidden. In instances where  there are multiple locations of hidden stored foods from which to choose,  they first  retrieve the food that they like the most, or which has the greatest abundance.

According to Angier, previous studies have shown that some pigs deceive their fellow pigs, by holding out on knowledge of where the choicest cache is hidden, and instead, lead them to a less desirable alternate, so as to reserve the best for themselves. This sort of deviousness is also, alack, another  pretty good indicator of pig intelligence.

Tony Stankus, FSLA, tstankus@uark.edu

Life Sciences Librarian, Science Coordinator & Professor

University of Arkansas Libraries MULN 223 E

365 North McIlroy Avenue

Fayetteville AR 72701-4002

Voice: 479-575-4031

Fax: 479-575-4592

 

Angier, N. (2009). Pigs prove smart, if not vain. New York Times,  (Tuesday, November 10, 2009),  p.D1, D3.

Bing, W., Bing, Y., Karim, M., HongHua, H., Yun, S., McGreevy, P., et al. (2007). Dietary sialic acid supplementation improves learning and memory in piglets. American Journal of Clinical Nutrition, 85(2), 561-569.

Broom, D.M., Sena, H., & Moynihan, K.L. (2009). Pigs learn what a mirror image represents and use it to obtain information. Animal Behaviour, 78, 1037-1041

Croney, C. (2000, August). Cognitive abilities of domestic pigs (Sus scrofa). Dissertation Abstracts International,  61, 598p.

de Jonge, F., Ooms, M., Kuurman, W., Maes, J., & Spruijt, B. (2008). Are pigs sensitive to variability in food rewards?. Applied Animal Behaviour Science, 114 (1), 93-104.

Drummond, H. (2006). Dominance in vertebrate broods and litters. Quarterly Review of Biology, 81(1), 3-32.

Grobbe, M., & Spek, G. J. (2009). Didactics for fauna managers, or how to teach wild boar to remain wild. / didactiek voor faunabeheerders, of hoe leer je wilde zwijnen wild te blijven. Vakblad Natuur Bos Landschap, 6(2), 24-25.

Held, S., Baumgartner, J., KilBride, A., Byrne, R., & Mendl, M. (2005). Foraging behaviour in domestic pigs (Sus scrota): Remembering and prioritizing food sites of different value. Animal Cognition, 8(2), 114-121.

Held, S., Mendl, M., Devereux, C., & Byrne, R. (2001). Studies in social cognition: From primates to pigs. Animal Welfare, 10,  209-SS217.

Jansen, J., Bolhuis, J., Schouten, W., Spruijt, B., & Wiegant, V. (2009). Spatial learning in pigs: Effects of environmental enrichment and individual characteristics on behaviour and performance. Animal Cognition, 12 (2), 303-315.

Jensen, P. (2009). In Jensen P. (Ed.), The ethology of domestic animals: An introductory text, modular texts. Wallingford; UK: CABI.

Kratzer, D. D. (1969).  Effects of age on avoidance learning in pigs. Journal of Animal Science, 28, 175-179.

Kratzer, D. D. (1971). Learning in farm animals. Journal of Animal Science, 32, 1268-1273.

Marchant, J., Whittaker, X., & Broom, D. (2001). Vocalisations of the adult female domestic pig during a standard human approach test and their relationships with behavioural and heart rate measures. Applied Animal Behaviour Science, 72(1), 23-39.

McLeman, M. A., Mendl, M. T., Jones, R. B., & Wathes, C. M. (2008). Social discrimination of familiar conspecifics by juvenile pigs, Sus scrofa: Development of a non-invasive method to study the transmission of unimodal and bimodal cues between live stimuli. Applied Animal Behaviour Science, 115(3), 123-137.

Nielsen, T., Kornum, B., Moustgaard, A., Gade, A., Lind, N., & Knudsen, G. (2009). A novel spatial delayed non-match to sample (DNMS) task in the Göttingen minipig. Behavioural Brain Research, 196(1), 93-98.

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