Kranz, V. A., Horback, K. M., Parsons, T. D. et al. 2022. Sow behavior during introduction to a large dynamic group is influenced by familiarity and method. Applied Animal Behaviour Science 250, 105624.
Sows in an extensive setting maintain small, stable matrilineal social groups comprised of familiar, and often genetically related, conspecifics. Providing conditions in an intensive farm setting which allow similar social groups could reduce aggression by allowing familiar sows to benefit from an established dominance order. Given that aggression levels among breeding sows peak immediately following introduction to a group pen, this study used a 2 × 2 factorial design to evaluate whether the level of familiarity among a small cohort, or method of introduction into a larger dynamic pen influenced the occurrence of aggressive behavior involving newly introduced sows. Treatments included combinations of sows either premixed for seven days prior to pen introduction (PMIX) or having no contact prior to pen introduction (UMIX) and entering the pen alone (IND) or entering the pen as a batch (BAT). Sows were monitored by focal video for one hour after entering the pen. Analysis of aggressive events yielded a significant interaction between level of familiarity and method of introduction. Familiarity had no effect when sows entered the pen as individuals whereas UMIX BAT sows participated in the most aggressive events (46.7 ± 9.1) and PMIX BAT sows the fewest (10.5 ± 2.1; P < 0.001). Overall, IND sows performed more retreats (3.6 ± 0.3) than BAT sows (2.8 ± 0.3; P < 0.01). PMIX sows spent more time lying with other sows (8.3 ± 1.7 min) compared to UMIX sows (1.9 ± 0.8 min; P < 0.05). PMIX BAT sows exhibited more nosing of other sows (47.9 ± 3.0) than their PMIX IND counterparts (37.6 ± 2.4; P < 0.001). These findings suggest that if small groups of sows are allowed to freely interact with each other prior to mixing into a larger dynamic group, even for as little as seven days, they can transition into the new social group with reduced rates of harmful aggressive behaviors and increased rates of affiliative behaviors. Future work should investigate whether premixed breeding groups maintain social affiliation throughout gestation, and thus, establish long-term subgroups within the larger pen.