Early-life microbial contact with adult hens modulates cecal microbiota and mitigates host responses to lipopolysaccharide-induced stress in broilers

Abstract Background In commercial production, the absence of adult hens disrupts natural gut colonization, forcing chicks to rely on environmental microbes and potentially compromising the ecological succession essential for health. This study investigated whether early-life adult hen microbial contact could optimize the intestinal community and metabolite profiles, thereby mitigating lipopolysaccharide (LPS)-induced immunological stress in broilers. Accordingly, 128 one-day-old broilers were assigned to control or adult hen microbial contact groups. Hens were removed on D 10, and LPS was administered on D 18 and D 20, resulting in a 2 × 2 factorial design. Results Adult hen microbial contact did not affect body weight or ileal histomorphology on D 10 or D 21. However, it reshaped the alpha diversity ( P < 0.05) and beta diversity ( P < 0.05) of the cecal microbiota, enriching beneficial genera such as Bacteroides , Prevotellaceae , Rikenellaceae , Muribaculaceae , and Megasphaera , although these were not primarily established through direct adult hen transfer. These microbial alterations were accompanied by increased production of cecal volatile fatty acids ( P < 0.05) and altered tryptophan metabolism ( P < 0.05), characterized by the conversion of serum tryptophan to indoleacetic acid. In the ileum, the adult hen microbial contact upregulated ( P < 0.05) genes associated with mucosal barrier integrity ( MUC13 , CLDN2 ) and antioxidant defense ( SOD2 , FOXO1 ), while independently downregulating ( P < 0.05) hepatic genes involved in redox regulation and autophagy ( GRX5 , LC3-1 ). LPS challenge induced a pronounced ( P < 0.05) antioxidant imbalance in the ileum, characterized by the downregulation of CAT and NRF2 , together with elevated expression of pro-inflammatory cytokines ( IL8 , IFNA , TNFA ), compromising barrier function ( MUC13 , CLDN2 ). Concurrently, the LPS challenge increased ( P < 0.05) the expression of hepatic genes involved in redox regulation and autophagy ( GRX5 , LC3-1 ), consistent with a systemic stress response. Notably, microbial contact attenuated the LPS-induced reduction in valeric acid ( P < 0.05), suggesting a protective effect on microbial metabolite production under immunological stress. Conclusion Adult hen microbial contact did not improve growth performance or ileal histomorphology, but shaped the early-life gut microbiota and associated metabolite profiles, contributing to improved resilience to subsequent immune challenges in broilers.