Seeing Pigs Through Rose-Colored Glasses


Late last week you might have seen headlines that went something like this:
"Pampered pigs 'feel optimistic'"
or, this: "Can you ask a pig if his glass is half full?"
or, "Pigs have feelings, too (and they prefer a bit of luxury)"

The headlines came, respectively, from BBC News, EurekAlert, and the Daily Mail.

This sounded pretty fishy to me. Optimism or pessimism requires a certain amount of introspection and future awareness. Without a meaningful sense of the future, optimism doesn't mean very much. I don't know much about cognition in pigs (and, for that matter, there hasn't been a ton of research on it), but I'm at best skeptical that pigs have the cognition required to plan for the future. I looked and looked for the original research that these articles were reporting on, but I could not find any. Finally, I found the original press release from Newcastle University. Surely a university PR office would do a more thorough job of reporting.

One thing was made clear by the press release: they were reporting not on published research, but on a poster that the Douglas lab had presented at the UFAW Animal Welfare Conference. Technically this is, indeed, peer reviewed, in some sense. Abstracts are vetted by conference committees, after all.

Babe may be the most famous sensitive pig in the world but new research from Newcastle University suggests he is by no means the only one.

Experts from the university's School of Agriculture, Food and Rural Development have shown for the first time that a pig's mood mirrors how content he is, highlighting that pigs are capable of complex emotions which are directly influenced by the environment in which they live.

Led by Dr Catherine Douglas, the team has employed a technique to 'ask' pigs if they are feeling optimistic or pessimistic about life as a result of the way in which they live.

Okay, so they developed a mechanism by which they can assess a pig's mood, and that mood seems to influenced by the environment. This is reasonable. But "a technique to 'ask' pigs if they are feeling optimistic or pessimistic about life?" Doubtful.

The press release continues:

The next step was to place half the pigs in an enriched environment - more space, freedom to roam in straw and play with 'pig' toys - while the other half were placed in a smaller, boring environment- no straw and only one non-interactive toy.

The team then played an ambiguous noise - a squeak - and studied how the pigs responded. Dr Douglas said the results were compelling.

"We found that almost without exception, the pigs in the enriched environment were optimistic about what this new noise could mean and approached expecting to get the treat," she said. "In contrast, the pigs in the boring environment were pessimistic about this new strange noise and, fearing it might be the mildly unpleasant plastic bag, did not approach for a treat.

The basic design was this: they took 10 pigs, and split them into two groups. One group was housed in an enriched environment: solid floor, lots of space, clean straw, lots of toys. Another group was housed in an environment designed to conform minimal legal standards: slatted floor, cramped space, one toy. Then, they were trained to associate one type of sound with food (thus forming a positive expectation upon hearing the sound), and a different sound with a visual or auditory startle (thus forming a negative expectation upon hearing the sound). Evidence that the associations had been formed were tested when, upon hearing the sounds, the pigs either did or did not approach the source of the sound, in order to receive the food reward, or avoid an unpleasant stimulus. Then, they were presented with a new ambiguous sound: would they approach, looking for food?

What this press release leads the reader to believe is that pigs who live in nice pens are "optimistic" about the new noise. They hope it will come with a reward. And pigs who live in deprived environments are "pessimistic" about the new noise, and shy away from it.

I sent an email to lead author Catherine Walsh to see if she would send me a copy of the poster. She didn't, but she did send me a copy of the abstract. Here's an excerpt:

Two groups, each of five gilts, were housed in either an enriched environment, with solid floor, extra space, clean straw, and a variety of toys, or a barren environment, a part-slatted pen conforming to minimum UK legislative standards. The consequences of change in environment were evaluated in a balanced 7-day cross over design. Pigs were initially trained to associate one auditory cue with a pleasant outcome (food) and another auditory cue with an unpleasant outcome (visual/auditory startle). Evidence of differentiation between the sounds was demonstrated in a go/no-go response (approaching a hatch for the pleasant outcome or not approaching when anticipating the unpleasant outcome). The pigs were then tested on two occasions following each housing change (into enriched or barren) using a novel ambiguous auditory stimulus to assess their cognitive bias. The hypothesis was that pigs in an enriched environment would demonstrate an "optimistic" bias, and pigs in a barren pen would show a pessimistic bias.

The key phrase above, that not a single one of the mainstream media accounts of this research mention is "consequences of change in environment."

Here's what really happened: the pigs who were living in the enhanced pen while learning the auditory associations were switched into the deprived pen, and the pigs from the deprived pen were switched into the enhanced pen. After switching pens, they were presented with the ambiguous auditory stimulus. Later, they were moved back to their original pens, and again tested with the ambiguous sound.

All group 1 pigs showed a reduced proportion of approaches in response to the ambiguous stimulus after moving from the enriched environment to the barren environment (P= 0.031, one tailed sign test), and increase to original response levels after return to the enriched environment. Group 2 pigs, which experienced the environments in the opposite sequence, showed mirror-image changes in response. Behavioural data from the home pen showed that pigs in enriched conditions exhibited more play and exploratory behaviours than those housed in the barren environment, who demonstrated more aggressive behaviours.

The pigs who were moved from the enhanced to the deprived environment were more reluctant to approach the ambiguous sound, but after returning back to their original enhanced environment, returned to baseline levels of approach. The pigs who started out in the deprived environment showed the exact opposite response. Both groups were more playful and exploratory while in the enhanced environment, and were more aggressive while in the deprived environment.

Are pigs who live in nice pens optimistic? Do they see the cup of life as half full? I'm not so sure. I think this experiment simply measured a behavioral response to the introduction or removal of environmental stressors. In a nice pen, free from stress and its physiological consequences, the pigs are happy to explore new sounds. In a stressful pen, with its physiological consequences, pigs are therefore reluctant to explore new stimuli, and are more aggressive. If this sounds familiar, it should. Remember the different stress responses in the domesticated foxes? I wrote,

Adrenaline is one hormone that is produced in response to stress, and controls fear-related responses. The experimental foxes had significantly lower adrenaline levels than their control-group cousins. The researchers hypothesized that foxes that are not afraid of humans are going to produce less adrenaline around them.

I would hypothesize that the differential responses by the pigs according to which environment they were in is probably related to this sort of physiological stress response as well. I look forward to reading the actual research paper that will emerge from this abstract and poster presentation.

The pigs in the enhanced environment weren't optimistic, they didn't see life through rose-colored glasses; they were more likely not stressed out, and had a reduced fear response. This by itself is really interesting research, as far as I'm concerned. To extrapolate optimism from these data and speak of "cups half full" and the like is, at best, disingenuous.

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By Birger Johansson (not verified) on 05 Aug 2010 #permalink

Thanks for posting about farm animal enrichment. It's a really interesting topic (and an important one, in my opinion).

My interpretation is this. I think the words "optimism" and "pessimism" were poorly chosen, but I believe I actually agree with the researchers' conclusions (assuming I understand them correctly). It is adaptive to be able to predict whether your environment is enriched and full of useful things (food, good places to nest, etc). In an enriched environment, exploring new things is a wise use of your energy resources, because there is a good chance whatever you discover will be useful to you. In an environment that is not enriched, this may instead be a poor use of your energy resources. So it's reasonable to think that pigs would behave differently in enriched vs unenriched environments, even if they can't perform tasks like introspection.

Your interpretation that the pigs in the unenriched environment were stressed is interesting, but I would want a little more discussion on possible mechanisms there. I'm not sure adrenaline would be the hormone to focus on here unless you're trying to say that the fight or flight response is involved. Stressed animals may trigger the SAM more easily and more strongly, but I'd be surprised if the explanation for why the unenriched pigs explored less was actual fear of the unknown noise. Your comparison to domesticated foxes also gives me pause; you're sort of comparing apples to oranges, right? Domestication is a genetic difference, but here we're talking about changes in individual animals when they change environments. Maybe the comparison is apt -- I would just want some more explanation before I'd go with it.

Part of the problem with these kinds of press releases of conference poster sessions is that you don't actually have the full research paper to examine. In this case, I had to directly seek out the author and got a copy of the abstract. So it's possible that many of these things are to be addressed.

I also thought it important to point out that the key here is *change* in environment. It would be interesting to know what would happen in individuals who did not change environments - e.g. pigs in the minimum legal standard environment. Are they indeed more "pessimistic" or whatever, or is it the change that drives this effect?

Last, I'm not suggesting that adrenaline is *the* hormone of interest, but more broadly that environmental stressors should be taken into account to provide a physiological basis for the differences in behavior.

"The pigs in the enhanced environment weren't optimistic, they didn't see life through rose-colored glasses; they were more likely not stressed out, and had a reduced fear response."

In people, it seems likely (although I don't know the research offhand) that basal general stress levels have a lot to do with one's location on the optimism/pessimism scale. I think the latter phenomenon you mention would be a good putative explanation of the former, if we had any reason to suppose that the former existed. I don't know the research on pig cognition very well, but I somehow doubt that we've unambiguously determined that pigs experience pessimism and optimism, those being (to come up with a quick working definition) specific attitudes that influence the appraisal of a situation in some way independent of the actual reward or punishment available.

@the dog zombie - It seems to me like a plausible explanation of the environmental impoverishment/stress connection is that in ecological conditions (that is, in wild ecosystems) animals are always "enriched" - enrichment is what we do to try to mimic the stimulation that animals evolved to cope with. A situation without that stimulation (such as in a plain laboratory enclosure) was probably encountered exceedingly rarely by the ancestors of pigs. It seems that many animals have evolved a need to explore and interact with various aspects of their environment, and lacking the ability to participate in this rewarding activity could lead to frustration, as well as all sorts of effects on neurodevelopment.

My point is, I guess, that a non-enriched enclosure is itself a very abnormal habitat, in the context of evolution. The brain may not have any mechanisms to deal with the paucity of stimulation offered by this environment, and so reacts the same way it reacts when any other basic need is not met - through specific reward-seeking behavior accompanied by/driven by/causing generalized stress.

As a disclaimer, this is mostly speculation on my part - purely armchair.

It's interesting speculation, though. What I was saying to Jason was "stress may be part of the mechanism, but how exactly?" I like your proposed answer.

may comment is i have a pig bat i dont have any think i want plan can u tall can how can i perotacte