According to researchers, the intensive breeding of pigs genetically predisposed to leanness has led some sows to develop classic symptoms of anorexia. They tend to be hyperactive and, in extreme cases, either refuse to eat at all or consistently eschew high fat in favour of low- energy foods. Many farmers believe such pigs are simply sickly one-off cases, while some veterinary specialists suggest that "wasting sow syndrome" is the outcome of poor husbandry.
However, according to John Owen, agriculture professor at Bangor University, a significant number of cases, particularly in Greece and the United States, cannot be explained simply by problems such as poor nutrition and housing. He suggests that selective breeding can dredge up rare and undesirable genes which unbalance the body's regulatory systems, affecting eating behaviour and leading to over-thinness. Since pigs bred for leanness are extra-sensitive to stress, such genes could be triggered by environmental factors such as poor living conditions, restricted food intake or a first pregnancy.
"The pigs will eat rubbishy food but avoid anything that makes them fat, in the same way that people who are anorexic might refuse to eat anything but lettuce," said Professor Owen, who has also found examples of similar conditions in goats and mink.
Eating disorder specialists at the Institute of Psychiatry in London claim the research on pigs is helping them unravel the origins of human anorexia. "There does seem to be a genetic disposition to leanness in the families of anorexics but vulnerability to the disorder is an interaction between genes and stressful events early in life or during puberty," said Dr Janet Treasure, a senior lecturer.
Researchers at the Institute are looking at how genes control the body's uptake of the brain neurotransmitter, serotonin, a chemical helping to govern mood. In a pilot study of 48 pairs of sisters - with an anorexic in each pair - they found that those with the disease were more perfectionist and had lower self-esteem than their sisters, as well as a higher proportion of particular serotonin receptors.
The wasting condition in pigs has already been treated with drugs that influence serotonin levels, but treatment for humans is more likely to concentrate on changing the environment and teaching flexible thinking.
Britons eat one million rashers of bacon a day, but while traditionally the choice was for fatty breeds, such as Tamworths, the present demand for leaner cuts has led to the domination of thinner hybrids.
Animal welfare campaigners have long argued that factory farming techniques cause distress but, despite recent legislation banning the stall and tether system for pregnant sows, pig farmers have been reluctant to make further changes. Modern agriculture ignores the natural inclination of pigs to live in family groups, and deprives them of their basic motivational drives for nesting and rooting.
The Institute of Psychiatry is looking for more pairs of sisters willing to take part in its ongoing studies of eating disorders.Reuse content