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Are pigs stupid? Perhaps they’re just stressed

The views expressed are those of the author and are not necessarily those of Scientific American.


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Average amount of meat consumed per person per year in the US (in pounds)

Pigs are one of the top animals consumed across the world. According to the US Census Bureau, in 2010, around one hundred million metric tons of pork were consumed that year, with 10% of this being in the US (although it does seem that overall meat consumption is declining).

With so many of us eating pork, you might think we’d know a bit more about these animals. A lot of people are surprised to hear about some of the cognitive abilities of the average pig. While it’s problematic to call an animal ‘intelligent’ or not, as this is a term is ill-defined and too often related to human cognition, pigs have shown us that they have a number of cognitive abilities tested across many different types of test. They have good learning and memory in many contexts (both short- and long-term), including episodic memory (memory for past events in their life), the ability to differentiate between familiar and unfamiliar pigs, and an inclination to explore novel objects.

A pig brain, taken from a Göttingen minipig

In addition to these behavioural feats, the pig brain is well-developed. For example, the volume of the prefrontal cortex is around 24% of the total neocortex and 10% of the total brain volume, comparable to primates including humans.

I’m not sure why, despite this research, pigs have a reputation for being ‘stupid’. Similar to the ‘three-second memory’ myth with fish, I wonder if it’s perpetuated to make people not feel bad about eating these animals, or the conditions under which they are often reared.

These conditions include not having enough space, being in barren environments bereft of stimulation and being denied the opportunity to perform their natural behaviours. In addition to this, many piglet’s tales are docked (80% of piglets in the UK), they have their teeth clipped, and males are castrated without anaesthetic (now banned in the UK but still legal throughout much of Europe).

Although many pigs are born outdoors, most will spend the rest of their life indoors

One recent study looked specifically at one aspect of pig rearing: how enriched the pigs’ environment was, to see its effects on the animals’ cognition. In particular, they looked at the effect of enrichment on the pigs’ spatial memory: the ability to remember where an object is.

Two groups of pigs were tested: one from ‘barren’ housing and one from ‘enriched’, which contained wood shavings, peat, straw and branches.

The task consisted of sixteen buckets, four of which had chocolate raisins in them (extremely yummy to pigs). The pigs were given access to these buckets over 30 trials, to see if they remembered where the chocolate was between trials, and how long it took them to learn this. To make sure that the pigs were actually remembering where the chocolate was and not just smelling it, all buckets had chocolate raisins placed under them under a mesh (to allow the odour through but not allowing the pigs to access them).

The pigs in the enriched housing did better on the task

The pigs housed in the barren pens were actually faster to reach the first baited bucket than the pigs from the enriched housing. This agrees with previous findings, and is thought to be because barren-housed animals are basically bored, and will work harder for food due to the lack of stimulation in their own pens. Additionally, the barren-housed pigs were just as good at remembering where the food was between the trials (using their long-term memory) as the enriched pigs. However, the barren-housed pigs had a worse short-term memory within each trial for the chocolate-rewarded buckets they had already visited and emptied, revisiting these buckets more often than the enriched pigs. The fact that the pigs’ housing condition affected short- but not long-term memory is interesting and supports the fact that these are different memory systems are underpinned by different neural substrates.

Rather than thinking of the enriched environment as enhancing the pigs’ cognitive abilities, the scientists instead present the poorer performance of the barren-housed pigs as a symptom of stress at their housing situation. This kind of ‘barren’ housing is common for pigs in many farms, and although consumers may not care if the pig they are eating is cognitively inferior to an enriched pig, they should care if the reason for this is due to stress or suffering caused to the animal.

 

References

Bolhuis, J. E., Oostindjer, M., Hoeks, C. W., de Haas, E. N., Bartels, A. C., Ooms, M., & Kemp, B. Working and reference memory of pigs (Sus scrofa domesticus) in a holeboard spatial discrimination task: the influence of environmental enrichment. Animal cognition DOI 10.1007/s10071-013-0646-7

Kornum, B. R., & Knudsen, G. M. (2011). Cognitive testing of pigs (Sus scrofa) in translational biobehavioral research. Neuroscience & Biobehavioral Reviews35(3), 437-451.

 

Photo credits

Meat graph by Angela Wong at NPR, data taken from here

Pig brain taken from Kornum & Knudsen (2011)

Pig with piglets: woodlywonderworks

Pig in house (photo not from experiment): Sean

German saddleback, a breed of domestic pig: Silke

Felicity Muth About the Author: Felicity Muth is an early-career researcher with a PhD in animal cognition. Follow on Twitter @notbadscience.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Xopher425 8:17 pm 06/11/2013

    I never thought pigs had a reputation for being stupid. They are known to frequently figure out different types of locking mechanisms on their pens and escape. It’s a different type of intelligence, definitely, and people certainly do dumb down animals (to avoid guilt of eating, most likely), and to preserve our self of superiority. I’ve even heard conjecture that, if humans were to disappear suddenly), pigs would eventually evolve to be the highest form of life on the planet, much the same way that early primates gave the rise to homosapians.

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  2. 2. Dani Boy 9:04 am 06/12/2013

    Xopher425 –

    I’ve never heard of this particular conjecture (?references?). It is simply impossible to predict this sort of thing, so let’s not pretend that pigs are Earth’s future overlords. :)

    What is ‘eventually’, and how do you define ‘highest form of life’?

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  3. 3. Bora Zivkovic 2:20 pm 06/12/2013

    This may differ from culture to culture. I grew up constantly hearing that pigs are, after dogs, most intelligent of all domesticated animals….

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  4. 4. Felicity Muth in reply to Felicity Muth 5:02 pm 06/12/2013

    Interesting. I’ve found with conversations with people that they seem surprised when I talk about pigs being ‘intelligent’ – but perhaps I’m just talking to the wrong people.

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  5. 5. Weaverdog 6:25 pm 06/12/2013

    I’ve raised pigs for the table, and pigs (pot-bellied ones) as pets. Pigs are smart, and I say that without the slightest hesitation — even after eating them. So, your suggestion that people deny porcine intelligence so that it’s easier to consume them is erroneous at least in my case.

    One point that you did not address is the “other side” of intelligence. Pigs are smart, yes, but they are amoral – at least as humans construct it. You mentioned tail docking, but you didn’t include the fact that piglets tails are removed by their handlers because of the risk of having tails EATEN by their fellow piglets. We can conjecture why piglets do this (free ranging piglets will, as well), but they do it and don’t seem at all bothered about the distress this causes to their siblings.

    Pigs also will maim or kill their human handlers — even otherwise docile pigs in free range situations with plenty of food and mental stimulation. Pigs in the wild also eat baby deer, and eat turkey and other ground-roosting bird eggs and hatchlings, as well. They don’t appear to be troubled by any moral qualms over this rather violent and pain-inducing behavior.

    Intelligence, problem solving, and evidence of complex cognitive processes are fine things. However, to me, that intelligence is not a barrier to making a fine meal of a pig…. that pig would have no hesitation in making a fine meal of me.

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