Hierarchy Establishment in Growing Finishing Pigs: Impacts on Behavior, Growth Performance, and Physiological Parameters

SIMPLE SUMMARY: Pigs are social animals that live in groups with well-established social structures and have always been a key species in debates over farm animal welfare. However, intensive production systems often fail to adequately consider pigs’ social needs. Group housing still presents major welfare concerns due to increased aggression for up to 48 h after pigs are mixed, with potentially chronic levels of aggression if stable social groups are not established. In our study we analyzed pig behavior, performance and physiological parameters after repeated mixing events. We compared individuals, using a dominance sociomatrix, and tested different hypothesis concerning pigs occupying different social ranking. The results suggest that hierarchical classification influenced feeding behavior and that pigs developed a possible compensation skill. Our findings highlight the importance of understanding the role of hierarchy and its biological relevance in group-housed pigs. Having a better understanding of individual differences, according to their social rank, may help producers and researchers identify and implement management strategies to reduce agonistic interactions and promote affiliative behaviors. ABSTRACT: In recent years, an increased number of studies have dealt with the analysis of social dominance related to animal behavior, physiology, and performance. This study aimed to investigate whether hierarchical ranking affects the coping style, non-social behavior during open field and novel object tests, performance, and physiological parameters of pigs. A total of 48 growing pigs (24 barrows and 24 females) were mixed three times during the growing–finishing period. The social and non-social behaviors of pigs were directly noted, and three behavioral tests were performed during the experimental period. Performance and physiological parameters were also recorded. Statistical analysis considered hierarchical classification (dominant vs. intermediary vs. subordinate) and p-values ≤ 0.05 were considered significant. After three regroupings, the pigs in different hierarchical classifications showed no change in hair cortisol values and open-field and novel object tests. Mean corpuscular hemoglobin concentration and leukocyte values increased in intermediary pigs, and the lowest counts were found in pigs classified as dominants. Furthermore, dominant pigs visited the feeder more but spent shorter time there compared to subordinate and intermediary pigs. Our results suggest that hierarchical classification influenced feeding behavior and physiological parameters without affecting cortisol values and growth performance, demonstrating a possible compensation skill.