Friend or foe: effects of social experience and genetic line on responses of young gilts in a social challenge paired interaction test.

The increased focus on group housing of sows in commercial pig production emphasises the importance of saving appropriate gilts which later become sows that are well-adapted to group housing systems. This study aimed to assess the short-term effects of social mixing experience and genetic line on social and exploration responses of young gilts in standardised 3-min social challenge paired interaction tests. The study included 96 gilts, from 26 litters, of two different genetic lines (Swedish Yorkshire and Dutch Yorkshire). These lines were chosen because the dam lines have been selected in group-housed and individual stall systems, respectively, a background which was hypothesised to have modified their social behaviour over time. The gilts were subjected to different early (opportunity to co-mingle with piglets in the neighbouring farrowing pen vs. no opportunity to co-mingle) and late (mixed with unfamiliar piglets at weaning vs. kept with familiar littermates after weaning) social mixing treatments, to test whether the enhanced social experience was beneficial in a socially challenging situation. Paired interaction tests were conducted at 5 and 20 weeks of age, and social and exploration behaviour of the gilts was recorded and analysed. The results showed that Swedish Yorkshire gilts explored the pen fittings more than Dutch Yorkshire gilts during the 5-week test, whereas Dutch Yorkshire gilts explored the pen fittings more than Swedish Yorkshire gilts during the 20-week test. No differences in play behaviour were found during the 5-week test, but in the 20-week test, gilts with early social mixing experience in their farrowing pen showed more locomotor play behaviour than gilts without this experience. Overall, these results suggest that genetic line and early social mixing experience can influence the social and exploration behaviours of young gilts in paired interaction tests. There was no support for the hypothesis that genetic selection in different housing systems has altered social behaviour, but it may have affected the level of exploration behaviour. There was little support for our prediction that early social experience has beneficial effects in a socially challenging situation.