Examining Factors That Predict Social Pairing Compatibility of Female Swine (Sus scrofa domesticus) in a Research Setting

Socially housing gregarious species enhances animal welfare by increasing affiliative interactions, exploratory behaviors, and other species-specific behaviors, while conferring decreased rates of abnormal behaviors. In addition, most regulatory guidelines promote social housing as a minimum standard to promote the wellbeing of the animals used in research. However, research performed to better understand the process of performing and evaluating social housing, particularly in research pigs, is severely lacking. Social housing does not come without risks, namely wounding during introductions. In this study, we aimed to assess predictors of agonistic and affiliative interactions between newly paired swine and to evaluate the use of a simple wound scoring system as a metric of the introduction process. We assessed whether the pigs’ relative weight difference or prior social experience influenced the behavior between pigs during the initial introduction and their longer-term compatibility as measured 72 h later. To further assess how stressful the pairing process was, we measured the pigs’ heart rate during social introductions. We accomplished this by recording data from 50 pairing events of female Yorkshire pigs. While agonistic behavior was observed in two-thirds of the pairing events, rates of agonistic behavior fell significantly by 72 h after pairing. In contrast, affiliative behavior was observed in more than three-fourths of the pairs at the initial introduction and rates remained equally high 72 h later. We found no correlation between the pigs’ weight difference and the rates of agonistic behavior observed, although prior pairing experience did mediate the rate of agonistic behavior observed such that previously paired pigs exhibited more agonistic behavior than did socially naive individuals. In addition, we validated the use of wound score as a proxy for more detailed observations of wounding behavior. Overall, we recommend socially housing female research pigs and allowing them to naturally sort out social rankings through interaction.