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However, when new groups are assembled, fighting can ensue. To help overcome this problem, Guelph researchers studied the influence of using a boar in group housing.

Other researchers found that a boar can be used to calm some pig groups. But the Guelph study shows this approach doesn't quell the aggression in pregnant sows.

Prof. Tina Widowski and graduate student Monica Séguin, Department of Animal and Poultry Science, say a boar's physical presence could actually increase stress levels in pregnant sows.

"To truly improve animal welfare, we need to find ways to reduce both stress and aggression," says Widowski. "Boars just aren't the solution."

In the study, a mature boar was grouped directly with 15 sows in the same pen. Another group of sows was exposed to a boar placed behind a fence in their pen. Researchers videotaped the arrangements and compared the footage to a sow group housed without a boar.

The researchers watched for signs of fighting and intensity of aggression, such as sows knocking heads or biting, as the pigs established their social hierarchy.

Widowski had expected the dominant boar presence would reduce fighting. But she says fighting was just as frequent with a boar as it was without one, with slightly less intensity. Boar presence also spiked sow stress levels - measured by an increase in the amount of stress-hormone found in each sow's saliva.

The boar's ineffectiveness to reduce aggression in pregnant sows compared to other groupings of pigs may be due to differences in size, age or the hormonal status of pregnant sows. Typically, the only time a sow would have exposure to a boar would be before mating, says Widowski.

This boar study is part of a larger group housing initiative being carried out at the University of Guelph's Arkell Research Station. In related studies, Widowski says Guelph teams have found that sows in the Arkell group housing system have larger litters and heavier piglets than those in gestation stalls in the same herd.

Funding for this research is provided by Ontario Pork, the Ontario Ministry of Agriculture, Food and Rural Affairs and the U.S. National Pork Board.

Others involved include Prof. Bob Friendship, Department of Population Medicine and collaborators at Michigan State University. Widowski's team is part of the Colonel K.L. Campbell Centre for the Study of Animal Welfare.

February 2007

Arthur Churchyard is a writer with SPARK, the University of Guelph's student writing program.