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2004 Swine Research Review

Herd Health and Management

Large Social Groups Exhibit Less Aggressive Behavior

Pigs with large social group experience display much less aggressive behavior compared to pigs living in small social groups.

Social traits of pigs in large-group settings have not been well understood. A study at the Prairie Swine Centre in Saskatchewan, Canada, attempted to corroborate expectations that pigs in larger groups adopt different social strategies than those in small social groups.

The experiment consisted of four pens of 18 pigs (small group or SG) and two pens of 108 pigs (large group or LG). Pigs were placed on fully slotted floors at about 70 lb., and given access to wet-dry feeders with a 9:1 pig-to-feeder space ratio.

Three studies evaluated aggressiveness of pig behavior.

The first study recorded the level of aggression for two hours, starting at 0, 24 and 48 hours following group formation.

In the second study, on Weeks 1, 6 and 12, a selected pair of pigs from a pen (SG or LG) was transferred to another pen (SG or LG). The aim was to assess the impact of moving pigs into different social structures on aggressive behavior. Patterns of aggressive behavior were monitored for two hours in a total of four different combinations involving 88 pigs/combination.

For the third study, after eight weeks, a total of 200 pigs were regrouped, four per group, in separate small pens for two hours. This allowed researchers to assess the effect of prior social experience (SG, LG) on aggression with known and unknown penmates from SG and LG accommodations.

As shown in Figure 1, there was no noticeable difference in the percentage of time that pigs spent fighting between the two group sizes up to 48 hours following grouping.

When pigs with large social group experience were mixed into an established large social group (LL), aggressive behavior was much less between the intruder and the resident pig than in other scenarios. Aggression was higher when pigs with large group experience were introduced to a small group (LS), when small group-experience pigs were introduced to a large group (SL), or when small group pigs were added to a small group (SS) (Figure 2).

When pigs were regrouped at Week 8, pigs from two SGs exhibited increased levels of aggression toward unfamiliar pigs, compared to those that came from two LGs. When pigs originating from SGs and LGs were combined, an intermediate level of aggression was observed (Figure 3).

Therefore, research suggests there is reduced aggressive behavior between pigs living in large social groups.

Researchers: Thusith S. Samarakone and Harold Gonyou, Prairie Swine Centre, Saskatchewan, Canada. Phone Samarakone at (306) 373-9922 or fax (306) 955-2510.

Click to view graphs.