By YUHI LI and LEE JOHNSTON
ST. PAUL, Minn. — With major pork buyers like McDonald’s, Hormel and Safeway announcing plans to move toward gestation stall-free suppliers, Minnesota hog farmers may be exploring group housing options.
Research through University of Minnesota Extension and the University of Minnesota West Central Research and Outreach Center in Morris, Minn. has uncovered the factors most likely to lead to success in group housing systems.
Unfamiliar sows fight for dominant status when mixed in a group. Since competition among sows is inevitable, management strategies should focus on minimizing competition and social stress for individual sows in a group.
Mix sows five weeks after breeding. Sows are less aggressive once pregnant compared with non-pregnant sows. In addition, aggression between two and three weeks after breeding can result in loss of embryos, which may cause reproductive failure.
Mix sows that were housed in the same group during the last gestation. Sows can remember their pen mates after a separation of four to six weeks, and will fight less when housed with sows they remember.
Sort by similar ages/sizes. Young sows are less aggressive than mature sows and suffer fewer injuries when housed separately.
When young sows have to be mixed with older sows, introduce a group of young sows that know each other to the pen and make young sows the majority in the pen.
Mix sows after feeding. Since limit-fed gestating sows fight for feed, aggressive interactions increase at feeding time.
Feed sows unlimited high fiber diets during the period of mixing. Sows with free access to feed containing high fiber content are less aggressive than limit-fed sows.
Consider boar intervention. Boars can suppress aggression among sows either due to the dominant status of the boar or the sexual distraction.
Increase group size. Although there is no optimal group size for minimizing aggression, sows in large groups have fewer fights per sow than small groups. It is possible that sows cannot form a social hierarchy in large pens due to too many pen mates. In addition, large groups are associated with large pens, which may allow subordinate sows to flee from fights or perform submissive behavior.
Provide spaces for subordinate sows to flee and hide from dominant sows in the pen. Form static groups. Once sows are mixed, do not add sows to the pen.
Avoid slippery or broken floors. The pen should have dry, even, and non-slippery floors to avoid leg injuries caused by fighting.
Get more guidance on transitioning to group housing at www.extension.umn.edu/swine.
(Yuzhi Li is an assistant professor at the University of Minnesota West Central Research and Outreach Center. Lee Johnston is a livestock educator with University of Minnesota Extension.)