This little piggy has depression

Scientists now say they can tell a happy animal from a sad one. But should this discovery inform the way we look after them? Sanjida O'Connell reports

Should we be using IQ as a benchmark for how we treat what we eat? Dr Michael Mendl, from Bristol University, has been studying pigs for 16 years and conducted a research project on the animals with Dr Suzanne Held, also from Bristol, and Professor Richard Byrne, from St Andrews. Mendl and Herne were mimicking experiments that had been performed on apes, which showed how similar primate intelligence is to human intelligence. Mendl was interested to see if studies such as these, showing just how smart apes, dolphins and monkeys were, would also show that farm animals were not intelligent. And, if so, could such findings justify our treatment of livestock?

Should we be using IQ as a benchmark for how we treat what we eat? Dr Michael Mendl, from Bristol University, has been studying pigs for 16 years and conducted a research project on the animals with Dr Suzanne Held, also from Bristol, and Professor Richard Byrne, from St Andrews. Mendl and Herne were mimicking experiments that had been performed on apes, which showed how similar primate intelligence is to human intelligence. Mendl was interested to see if studies such as these, showing just how smart apes, dolphins and monkeys were, would also show that farm animals were not intelligent. And, if so, could such findings justify our treatment of livestock?

Traditionally, scientists searching for insight into animal intelligence have tended to equate a high IQ with a level of consciousness analogous to our own. But Professor Marian Dawkins, an animal behaviourist at Oxford University, argues that there is a "pitfall" in linking consciousness to intelligence. Mendl agrees. "There is an implicit assumption that the more clever an animal is, the more likely it is to suffer, and I'm not sure that there is a clear link between the two," he says. An accurate assessment of how animals feel, as well as how they think, is vital to ensure a high standard of animal welfare, he says.

There have been a number of sophisticated studies designed to assess consciousness and cognition. In one American experiment, humans and animals had to observe a box on a dark computer screen containing a variable number of illuminated pixels. The subjects had to indicate whether that box contained a high density of pixels (more than 2950) or a sparsity (up to 2949), which became harder in the middle range, moving, say, between 2950 and 2949. The subjects could also indicate that they were uncertain.

Humans, monkeys and dolphins were able to perform this task, the humans and monkeys using buttons or levers and the dolphins using paddles. And the ability to indicate that they didn't know the answer, in response to the harder tests, showed that members of all three species had a degree of mental awareness. Scientists sometimes equate this kind of intelligence with self-awareness - a high degree of consciousness. Rats and pigeons, however, were unable to use the "uncertain" key, which may mean that they are not conscious of their thoughts.

However, an animal that is not aware of its thoughts may still be aware of its feelings and emotions. An awareness of sensations and emotions is known as "feelings consciousness". As far as welfare is concerned, this is the crux of the matter: what an animal feels, not just what it thinks.

"Animals like us that are clever are more likely to suffer because they can think about suffering in the future and remember suffering in the past. But they are also capable of understanding that pain is going to stop. Less intelligent animals may not have this capacity," says Mendl. They may, therefore, be worse off because they suffer not knowing their pain can end.

How can we tell what an animal feels? We may never know for certain because feelings, even those of our nearest and dearest, are often private experiences. However, experiments based on what is known about human emotions help. Mendl and Drs Emma Harding and Elizabeth Paul, also from Bristol University, have devised a test based on assessing human "feelings consciousness" and made it applicable to rats. "What we're doing is looking at humans as a model for animals," says Paul. The team are interested in determining whether rats react like people when they are depressed. "Depressed, anxious people judge ambiguous events negatively - this is a very clear and robust finding in clinical psychology," says Paul.

First, the researchers trained rats to respond by pressing a lever when they heard a "good" tone. The rats learnt that if they did this they would be rewarded with a food pellet. They were taught not to press the lever when they heard a different "bad" tone; if they succeeded, they avoided hearing white noise. Half the rats were then put in unpredictable cages where lights sometimes turned on or off unexpectedly, which the researchers thought would induce a mildly negative mood. All the rats were then played a tone that was ambiguous, with a frequency between the good and bad tone. What the team found was that the "depressed" rats reacted most often to the new tone as if it were a negative stimulus - as if they would hear white noise, whereas the happy rats reacted as if the tone was positive and they would receive a food reward. Mendl says: "These findings parallel those of humans and suggest a completely new method for measuring animal emotions."

Another way to tap into an animal's emotions is to train them to communicate how they feel. A group of researchers from London taught pigs to give one response when they felt normal and a different response when they were anxious (in this case they were given a drug designed to induce temporary anxiety). Not only could the pigs discriminate between these two states, but later they made the same "anxious" response when exposed to novel events such as an unfamiliar pig or a new pig pen. It seems that, since pigs are smart enough to tell researchers how they feel, they could be trained to understand that although a routine husbandry procedure might be frightening, it could be over relatively quickly and painlessly.

Procedures such as tail docking in sheep and branding in cattle are thought to be very painful because animals respond in a way we associate with pain. Although highly subjective on our part - we have no idea what any animal really feels - physiological studies show that when reacting as if in pain, animals' stress hormones soar.

Professor Dan Weary, from the University of British Columbia, argues that conventional husbandry methods should be rethought on the basis of the animals' reactions. In one experiment, half the male piglets on a farm were castrated and the other half were handled as if they were going to be. Only the pigs who were castrated made high-pitched squeals, and only at the time of the castration. Some farmers believe that the younger the animal, the less painful the operation, but these pigs squealed no matter what age they were. The experiment indicates that animals calls are a good way of assessing their actual pain, rather than the expectation of pain.

Castration is performed - though rarely in Britain - because male hormones produced by the testes are stored in the pigs' body fat and give the meat an unpleasant taint. But castration, as well as being time-consuming, reduces the growth rate and results in poorer quality meat. Weary suggests that pigs should be injected with hormones that neutralise the sex hormones - "immunocastration" - instead of being painfully castrated.

Mendl and his colleagues' are still exploring "feelings consciousness" in pigs as well as their capacity for intelligence, in an effort to improve animal welfare on commercial farms. One of his studies indicates that pigs become stressed by normal farm management techniques, such as constantly meeting unfamiliar individuals, or by being weighed. This level of stress can make pigs forgetful.

The findings of other researchers support this conclusion: stress hormones in animals and humans can disrupt memory. It might seem esoteric - having farms full of forgetful pigs - but you could argue that the ability to process information and store memories is related to conscious experience. On the other hand, even if pigs have no consciousness, forgetfulness can lead to damaging behaviour and inefficient husbandry. For example, animals with impaired memories might attack individuals because they have forgotten they know them. This often happens when sows that have given birth are reunited with their mates; they often fight vigorously.

Just over nine million pigs are slaughtered each year in the UK. While many are kept outdoors, unlike other animals, there are still important welfare problems to be tackled. Tail-biting and other forms of aggression are commonplace and may be exacerbated in barren environments where the pigs have no access to straw. Sows kept indoors are confined to crates so narrow that the mother pig cannot turn around during the lactation period.

By looking at how animals feel as well as what they think, scientists may be able to enhance animal welfare. One day, perhaps, scientists such as Mendl may be able to tell us exactly what matters to a pig.