Sow aggression under spotlight
STALLS and tethers are a thing of the past. But as one welfare problem is solved, another arises – sows mixed after weaning fight. There are no simple answers and changing mixing pen dimensions is unlikely to help, according to research at ADAS Terrington.
Sows on a MAFF-funded trial were placed in pens of different shapes and sizes, to measure the effect on aggression, says ADAS researcher Roger Kay.
"Four pen shapes were used with two different stocking densities, 4.1m sq a pig and 9.3m sq a pig. We thought that pigs with more space might be better able to avoid aggression. Each pen contained six sows."
At each stocking density, pens covered the same floor area but had different length to width ratios – 4:1, 2:1, 1:1 and a circle. Longer pens were believed to offer sows a better chance of avoiding aggression by allowing them to flee further from the most aggressive sows, according to Mr Kay.
But the trial showed that stocking density and pen shape had no effect on aggression. "Skin damage was used to measure the outcome of aggression and was the same for all treatments. This means the higher stocking density of 4.1m sq a pig is equally acceptable to the lower stocking density of 9.3m sq for mixing sows," he adds.
So how long can producers expect sow aggression to last? "Aggression, manifested as brief encounters, one-sided or two-sided fights is worst in the first four hours after mixing. After 24 hours it is minimal and sows can be moved into service areas," advises Mr Kay.
The next stage of the project will look at the effect of boar presence and group size on sow aggression. *