摘要Background Accumulating evidence from human trials and rodent studies has indicated that modulation of gut microbiota affects host physiological homeostasis and behavioral characteristics.Similarly,alterations in gut micro-biota could be a feasible strategy for reducing aggressive behavior and improving health in chickens.The study was conducted to determine the effects of early-life cecal microbiota transplantation(CMT)on cecal microbial composi-tion,brain serotonergic activity,and aggressive behavior of recipient chickens.Methods Chicken lines 63 and 72 with nonaggressive and aggressive behavior,respectively,were used as donors and a commercial strain Dekalb XL was used as recipients for CMT.Eighty-four 1-d-old male chicks were randomly assigned to 1 of 3 treatments with 7 cages per treatment and 4 chickens per cage(n=7):saline(control,CTRL),cecal solution of line 63(63-CMT),and cecal solution of line 72(72-CMT).Transplantation was conducted via oral gavage once daily from d 1 to 10,and then boosted once weekly from week 3 to 5.At weeks 5 and 16,home-cage behavior was recorded,and chickens with similar body weights were assigned to paired aggression tests between the treat-ments.Samples of blood,brain,and cecal content were collected from the post-tested chickens to detect CMT-induced biological and microbiota changes.Results 63-CMT chickens displayed less aggressive behavior with a higher hypothalamic serotonergic activity at week 5.Correspondingly,two amplicon sequence variants(ASVs)belonging to Lachnospiraceae and one Ruminococ-caceae UCG-005 ASV were positively correlated with the levels of brain tryptophan and serotonin,respectively.72-CMT chickens had lower levels of brain norepinephrine and dopamine at week 5 with higher levels of plasma serotonin and tryptophan at week 16.ASVs belonging to Mollicutes RF39 and GCA-900066225 in 72-CMT chickens were nega-tively correlated with the brain 5-hydroxyindoleacetic acid(5-HIAA)at week 5,and one Bacteroides ASV was negatively correlated with plasma serotonin at week 16.Conclusion Results indicate that CMT at an early age could regulate aggressive behavior via modulating the cecal microbial composition, together with central serotonergic and catecholaminergic systems in recipient chickens.The selected CMT could be a novel strategy for reducing aggressive behavior through regulating signaling along the microbiota-gut-brain axis.