Social order is an important part of many animal species’ lives. Social aggression helps determine hierarchy of the animals and which animals are pushed to the bottom of the pecking order. Pigs are mixed into new social groups throughout various stages of production. Therefore, their hierarchies have the opportunity to change numerous times during their lives. In this experiment, Ison and colleagues looked at the social interaction when a mixed group of primiparous and older, unfamiliar sows were placed in group housing together.
Why group housing?
Pig farmers can choose to use either independent or group housing for their pregnant sows, however in recent years, there has been a push towards group housing. This is due to the fact that in group housing, sows are able to perform more normal behavior than they are in individual stalls. In Europe, gestation stalls can only be used for up to four weeks after breeding. In group housing, sows are able to move around freely. In this experiment, the gilts, female pigs who had never given birth before, were kept with other gilts until the most recently bred pig had reached 39 days of gestation. Then half of each of the primiparous groups (first-time mothers) was selected and mixed with multiparous sows for a week. After this week, they went back to their home pens. A week later, they were mixed with other multiparous sows for a week, before moving back to their home pens once again. This experiment reflects how often switching can occur in the social group groups of pigs throughout production.