From feather pecking to immunity: Immune differences between lines selected for high and low feather pecking.

Feather pecking (FP) is a serious behavioral disorder in laying hens, leading to feather damage, skin lesions, and often resulting in cannibalism. The mechanisms underlying FP are not clear yet, but recently the role of the immune system as a cause has been discussed. In humans, the interrelation between personality traits and the immune system is well-documented, with impulsivity and hyperactivity linked to distinct alterations in blood immune cell numbers and to elevated levels of pro-inflammatory cytokines. Similarly, FP in hens is associated with impulsivity and hyperactivity, suggesting a possible connection between FP and immune cell alterations. In this study numbers of leukocyte subsets in blood, spleen and cecal tonsils, along with mitogen-induced lymphocyte proliferative response and antibody concentrations across hens selectively bred for high (HFP) and low (LFP) feather pecking behavior were analyzed. Results showed that divergent selection altered FP behavior, with HFP hens showing about 10 times more pecking behavior than hens of the LFP line. HFP hens had lower numbers of T helper cells, CD4+ CD25 as well as B cells compared to LFP hens. Furthermore, HFP hens demonstrated a stronger proliferation of T cells when stimulated with ConA, while showed a weaker response in T cell-dependent B cell proliferation when stimulated with PWM, compared to LFP hens. Antibody plasma concentrations were similar between both lines. These findings highlight substantial immunological differences between HFP and LFP hens, especially in T cell immunity, and support the hypothesis that FP may be an immune-related behavioral response.