When the pigs on a farm in North Jutland suddenly began behaving erratically for no apparent reason, Esben Larsen from DTU Electrical Engineering set out to find the cause, which may have something to do with electric current.
A few years ago, a pig farmer in North Jutland began to notice problems with pigs suddenly displaying strange behaviour such as crying out and attempting to run away. A whole series of veterinarians and other experts were unable to come up with a plausible explanation. The farmer himself suspected that it might have something to do with electric current, so he contacted DTU where he was fortunate enough to bump into Associate Professor Esben Larsen, a bright spark at DTU Electrical Engineering. The researcher had his doubts about the farmer’s theory, but nevertheless agreed to put together a study in partnership with the Danish Pig Research Centre—known as SEGES today—and Aalborg University.
“I’m the son of a farmer from North Jutland, and I really felt for this family, struggling to ensure the welfare of their pigs. So I set up a major measurement programme, involving installing data loggers in two of the sties,” relates Esben Larsen.
As far as he can make out, the current in the sties stems from several sources, including external sources—known as ‘wandering current’—and internal sources inside the sties themselves, through what can best be described as the ‘manure battery’.
“Statistically, there is a risk that a pig can form part of an electrical circuit when it drinks from a drinking nipple made of zinc while simultaneously peeing on a cast iron grating,” he explains.
“Together, zinc, iron and bodily waste form a galvanic element (a battery) that can generate current of around 0.7 volts, which is less than in a bicycle light battery. We measured resistance in the animals—in the presence of a veterinarian, of course—and determined that it is around 400–800 ohms, which means that the pigs might be subjected to a jolt of around a milliampere. But is that enough to cause discomfort?”
More sensitive than people
It seems that this may be the case, as it is well-known that animals are much more sensitive to electrical current than people. A human being suffers a severe shock at a level of 10 milliamperes, so it is not unlikely that pigs may feel discomfort if they receive a little shock from the manure battery. Moreover, there is the signficant difference that a sow cannot simply run out of her pen if she feels discomfort— which may well result in her feeling stressed.
Manure batteries may be created in most pig sties, but this is not to say that pigs form part of an electrical circuit in all areas of the sty. It all depends on how the sty is designed.
“We have proved it is likely that an electrical circuit could be formed in the North Jutland facility when pigs drink and pee at the same time, and that this may contribute to the pigs’ reactions. However, we have not found a statistical basis to prove that the manure battery is the only cause of the problem,” concedes Esben Larsen.
Today, two years and six million datasets down the road, he is unfortunately obliged to concede that he cannot present an unambiguous explanation for the pigs’ discomfort.The project has been brought to a close and the report written, but the problem has not been solved. Esben Larsen is not convinced that the manure battery phenomenon is the whole story. There may also be what is known as ‘wandering current’ in the soil. Fluctuations were recorded on a number of earth spikes outside the farm, but here, too, researchers were unable to establish a direct correlation with the pigs’ reactions.
It may be a statistical anomaly, but Esben Larsen has no doubt that there is something wrong on the farm in North Jutland, and he is committed to helping out. In fact, he has now developed a large system that is designed to measure wandering current, and which is currently standing in DTU Electrical Engineering’s back yard.
He hopes to be able to raise funds to take measurements at several locations in Denmark, because many people are complaining of problems with earth current—in connection with wind turbine installations, for instance.
“The phenomenon has not yet been scientifically described. So I intend to take care of it,” concludes Esben Larsen.