摘要Butyrate promotes the growth and gastrointestinal development of calves.But,the mechanisms behind its effects on signaling pathways of the gastrointestinal tract and rumen microbiome is unclear.This study aimed to reveal transcriptomic pathways of gastrointestinal epithelium and microbial community in response to butyrate supplementation in calves fed a high fiber starter.Fourteen Holstein bull calves(39.9±3.7 kg,14 d of age)were assigned to 2 groups(sodium butyrate group,SB;control group,Ctrl).The SB group received 0.5％SB supplementation.At d 51,the calves were slaughtered to obtain samples for analysis of the transcriptome of the rumen and jejunum epithelium as well as ruminal microbial metagenome.Sodium butyrate supplementation resulted in a higher performance in average daily gain and development of jejunum and rumen papillae.In both the rumen and jejunum epithelium,SB down-regulated pathways related to inflammation including NF-κB(PPKCB,CXCL8,CXCL12),interleukin-17(IL17A,IL17B,MMP9),and chemokine(CXCL12,CCL4,CCL8)and up-regulated immune pathways including the intestinal immune network for immunoglobulin A(IgA)production(CD28).Meanwhile,in the jejunum epithelium,SB regulated pathways related to nutritional metabolism including nitrogen metabolism(CA1,CA2,CA3),synthesis and degradation of ketone bodies(HMGCS2,BDH1,LOC100295719),fat digestion and absorption(PLA2G2F,APOA1,APOA4),and the PPAR signaling pathway(FABP4,FABP6,CYP4A11).The metagenome showed that SB greatly increased the relative abundance of Bacillus subtilis and Eubacterium limosum,activated ruminal microbial carbohydrate metabolism pathways and increased the abundance of carbohydrate hydrolysis enzymes.In conclusion,butyrate exhibited promoting effects on growth and gastrointestinal development by inhibiting inflammation,enhancing immunity and en-ergy harvesting,and activating microbial carbohydrate metabolism.These findings provide new insights into the potential mechanisms behind the beneficial effects of butyrate in calf nutrition.