Stereotypic behaviors are associated with physiology and immunity differences in long-term confined sows

Pregnant sows in the confined environment have poor welfare and frequently perform stereotypic behaviors. In order to clarify whether highly stereotypic behavior is a sign of increased stress and successfully contributes to coping with or adaptation to adverse environment, fifty pregnant sows (Large White × Landrace) housed in stalls were selected to observe behaviors and analyze physiological parameters [cortisol, major acute phase protein (Pig-MAP) and C-reactive protein (CRP)], and immunological parameters [immunoglobin A (IgA), immunoglobin G (IgG), interleukin 6 (IL-6), interleukin 10 (IL-10), tumor necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ)] in early, middle and late gestation (27th, 62nd and 91st day). A repeated-measures analysis and Friedman test was performed to analyze the differences of behaviors and physiological and immunological parameters. The results showed that lateral lying behavior increased significantly with the progress of sows' gestation, while standing and ventral lying behaviors significantly decreased (p < 0.05). Sham-chewing, bar-biting, trough-biting and rooting behaviors significantly reduced (p < 0.05). Furthermore, there was no significant difference in physiological and immune levels in different gestational periods (p > 0.05). The results also indicated that sham-chewing behavior was positively correlated with serum cortisol, IL-6, IL-10, and negatively correlated with serum IFN-γ in each gestational period (p < 0.05). Trough-biting behavior was positively correlated with serum TNF-α in middle and late gestation (p < 0.05). Rooting behavior was positively correlated with serum IgG in each gestational period, and positively correlated with serum Pig-MAP, IL-6, and IL-10 in middle and late gestation (p < 0.05). In conclusion, the sows with a high incidence of stereotypic behaviors tried to improve stress and humoral immunity to cope with the confined environment, and long-term confined sows might be in a chronic stress state.