Abstract: 【Object】 This experiment aimed to explore innovative feeding resources and enrich the basic data of feed mulberry research.【Method】 One hundred and ninety-two Yellow-feathered chickens at 43 days old were randomly divided into 4 groups with 6 replicates in each group and 8 birds per replicate.The chickens in control group were fed with the basal diet,and those in three fermented groups were fed with 3%,6% and 9% fermented feed mulberry,respectively,replacing the same amount of the basal diet.The experiment lasted for 42 days.At the end of the experiment,cervical venous blood,intestinal tissues and cecal contents of Yellow-feathered broilers were collected to determine serum biochemical indexes,intestinal tissue morphology,and cecal microflora,respectively.【Result】 Compared with the control group,①The serum glucose (GLU) levels of chickens of 6% and 9% fermented groups were increased significantly (P＜0.05).②The villus height and crypt depth of the duodenum of 9% fermented group,the villus height of the jejunum of 3 test groups,the villus height to crypt depth ratio (V/C) of jejunum of 3% and 6% fermented groups and the V/C of the ileum of 6% fermented group were decreased significantly (P＜0.05).③The ACE index and Chao1 index of 9% fermented group were decreased significantly (P＜0.05),and the Shannon index of 6% fermented group was increased significantly (P＜0.05).The Beta diversity analysis showed that the cecal microbials composition of 6% and 9% fermented groups were significantly different.At phylum level,the relative abundances of Firmicutes,Epsilonbacteraeota,and Tenericutes in the cecum of 6% and 9% fermented groups were increased significantly (P＜0.05),while the relative abundances of Kiritimatiellaeota,uncultured_bacterium_k_Bacteria,Verrucomicrobia of 6% and 9% fermented groups,and Bacteroidetes of 9% fermented group were decreased significantly (P＜0.05).At genus level,the relative abundances of Campylobacter,[Ruminococcus]_torques_group,Faecalibacterium in cecum of 6% and 9% fermented groups were increased significantly (P＜0.05)，while the relative abundances of uncultured_bacterium_o_WCHB1-41,uncultured_bacterium_f_Clostridiales_vadinBB60_group,and uncultured_bacterium_k_Bacteria in cecum were decreased significantly (P＜0.05).In addition,the relative abundances of Megamonas,Ruminococcaceae_UCG-014,Prevotellaceae_UCG-001,Megasphaera,and uncultured_bacterium_f_Firmicutes_bacterium_CAG_822 in cecum of 9% fermented group were increased significantly(P＜0.05),while the relative abundances of Rikenellaceae_RC9_gut_group and uncultured_bacterium_o_Bacteroidales in cecum were decreased significantly(P＜0.05).The differential prediction of KEGG function of cecal microbials showed that the metabolic pathways of ABC transporters and pyrimidine metabolism of 6% and 9% fermented groups were up-regulated significantly(P＜0.05),while the metabolic pathways of biosynthesis of secondary metabolites were down-regulated significantly (P＜0.05).【Conclusion】 The basal diet containing 6% and 9% fermented feed mulberry significantly increased the serum GLU level of Yellow-feathered chicken,had a negative effect on intestinal tissue morphology，and significantly increased the relative abundance of Firmicutes in cecum,etc.Under the conditions of this experiment,the appropriate amount of fermented feed mulberry should be controlled at 6% or below.

Key words: fermented feed mulberry; Yellow-feathered chicken; serum biochemical indexes; intestinal tissue morphology; cecal microflora