**6. Conclusions**

Our data suggest that dietary inclusion of probiotics has positive effects on reducing agonistic behaviors in laying hens through modification of the serotonergic system without negative effects on growth and production performance. The data indicate that dietary probiotic supplementation could be a useful management tool for preventing aggressive behaviors in laying hens. In addition, the current chicken strain could be a useful model to investigate mechanisms underlying the potentially probiotic therapy for preventing and reducing emotional susceptibility associated with psychiatric disorders such as depression and anxiety in humans.
