Friday, 6 July 2012

Do factory-farmed pigs know what they are missing?


You have probably heard this argument many times in defence of the factory farming industry:  if animals have never experienced any better conditions, then that means they don’t know what they are missing and therefore they are not suffering. But is this really true?

Does the fact that animals are always kept in barren conditions mean that they really “don’t know any better” and therefore it is OK?

I don’t think so… and a recent study has provided evidence that animals kept in barren conditions, without ever having experienced good conditions, are in a bad emotional state and are suffering.

In this experiment, two groups of young pigs were randomly assigned to housing in either an enriched or barren environment. The barren environment was pretty typical for factory farming and met the minimal requirements for intensive pig housing according to EC directives. The pigs had 1.2m2 space each, the pens had a partially slatted concrete floor and there was a wood log to play with. Pigs in the enriched environment were kept on a solid concrete floor (1.9m2 space per pig) covered with fresh straw and had metal chains and logs, sticks and cardboard boxes to play with.

Pigs were then trained on a judgement bias task. The judgement bias methodology comes from human psychology and has recently been adapted to measure emotional states in animals. It is a very promising methodology. It basically measures whether the animal perceives its environment as “optimistic” or “pessimistic”. It is kind of a glass half full or half empty type of test.

Pigs were trained to associate a note played on glockenspiel with a tasty food reward (apple): when they heard the note they had to approach a hatch in a training arena were they received an apple.  They were also trained to associate the sound of a dog clicker trainer with an aversive event (a plastic bag waved in the face). When pigs approached the hatch, the bag was waved in their face, which then taught them NOT to approach the hatch when hearing the dog clicker trainer.  Once the pigs had learned to always approach the hatch after hearing the glockenspiel but never to approach when hearing the clicker trainer they were ready for the judgement bias test.

In the judgement bias test, a third unfamiliar sound was played (a squeaky dog toy) and it was observed whether the pigs approached the hatch or not. A pig expecting to be rewarded with the apple approached the hatch after hearing the ambiguous sound, and therefore made an optimistic choice. While pigs expecting to be punished by the plastic bag did not approach the hatch, and made a pessimistic choice.

The results of the study were very interesting. The first time judgement bias was tested, the pigs kept in the barren environment approached the hatch significantly less often compared to the pigs kept in the enriched environment.

This shows that even though the barren-housed pigs had never experienced any enriched conditions, they interpreted the ambiguous sound as more pessimistic and were expecting to be punished more often! In humans, such pessimistic interpretation of events is often seen in depressed people!

After the first test, the housing of the pigs was then changed: pigs in the enriched group were moved to barren housing and the pigs in the barren group were now housed in enriched pens.

The next judgement bias test again showed that pigs kept in the barren conditions interpreted the ambiguous sound as more pessimistic.

The pigs were then changed back to their original housing, and results were similar.

The study also found that the length of time that pigs experienced the housing conditions affected how they interpreted the ambiguous cues.  Pigs that had been housed in the enriched environment for 5 weeks made more pessimistic choices when moved to the barren environment than pigs that had experienced the enriched conditions for only 7 days. It seems that once the animals are used to the enriched conditions, it is worse to experience the barren conditions.

Therefore, pigs that never experienced enriched conditions appear to know what they are missing. But pigs that do know what they are missing are affected by barren housing even worse!

So there is really no excuse for keeping pigs in barren environments! 

I wonder how these free-range pigs would have
interpreted the ambiguous sounds? I guess they would
have been pretty optimistic!
Reference: Douglas et al., 2012. Environmental enrichment induces optimistic cognitive biases in pigs. Applied Animal Behaviour Science. Article In Press. 

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