Mixed Management in Growing and Finishing Pigs: Impacts on Social Behavior and Judgment Bias.

Intensive pig production practices may shape cognition and behavior. We evaluated whether repeated regrouping (mixing) and gender (gilts vs. barrows) affect social interactions, fear-related responses, and affective state. A total of 96 growing pigs were separated into two treatments: control-pigs that were mixed once during the growing-finishing period; and social stress-pigs that were mixed thrice during the growing-finishing period. Social and non-social behaviors were directly noted, and four behavioral tests were conducted: open field, novel object, couples, and judgment bias tests. The statistical analysis compared gender and treatment, and p-values ≤ 0.05 were considered significant. Females stayed longer in the test pen entrance area during the novel object test and barrows spent more time at the feeder and defecated more during the couples' test. With regard to the judgment bias test, females took longer to be considered trained in the discriminatory learning task and presented a "pessimistic judgment" during the ambiguous cue. Our results suggest that gender influences judgment bias in pigs and can influence social and non-social behavior, which may reflect a negative affective state with implications for their welfare and management.