Time budgets of group-housed pigs in relation to social aggression and production.

Commercial producers house growing pigs by sex and weight to allow for efficient use of resources and provide pigs the welfare benefits of interacting with their conspecifics and more freedom of movement. However, introduction of unfamiliar pigs can cause increased aggression for 24-48 h as pigs establish social relationships. To address this issue, a better understanding of pig behavior is needed. The objectives of this study were to quantify time budgets of pigs following introduction into a new social group and how these changed over time, and to investigate how social aggression influences overall time budgets and production parameters. A total of 257 grow-finish Yorkshire barrows across 20 pens were introduced into new social groups at 10 wk of age (~23 kg) and observed for aggression and time budgets of behavior at 4 periods: immediately after introduction, 3, 6, and 9 wk later. Pigs were observed for duration of total aggression and initiated aggression (s) for 9 h after introduction and for 4 h at 3, 6, and 9 wk later. Time budgets were created by scan-sampling inactive, movement, ingestion, social, and exploration behaviors every 2 min for 4 h in the afternoon and summarizing proportion of time each behavior was performed by period. Least square means of each behavior were compared across time points. Pigs spent most of their time inactive. In general, the greatest change in pig behavior was observed between introduction and wk 3 (P<0.003), with gradual changes throughout the study period as pigs became more inactive (wk 3 vs. wk 6: P=0.209; wk 6 vs. wk 9: P=0.007) and spent less time on other behaviors. Pigs' non-aggressive behavior and production parameters were compared to aggression using generalized linear mixed models. The time pigs spent on non-aggressive behaviors were negatively related to aggression (P<0.045) with few exceptions. Initiated aggression after introduction was negatively related to loin muscle area (P=0.003). These results show how finishing pigs spend their time in commercial facilities and indicate that behavior continues to change for up to 9 wk after introduction to a new social group. Efforts to reduce chronic levels of aggression should focus on promoting non-aggressive behaviors, such as exploration and movement, after the initial fighting that occurs immediately after introduction has waned and should be implemented for up at 9 wk after introduction into new social groups.