Abstract: 【Objective】 This experiment was conducted to investigate the effects of steam-flaked corn on the weight gain,rumen fermentation and microbial community of Xinjiang Brown cattle, and to explore the feeding methods to improve the weight gain performance and feeding efficiency of beef cattle.【Method】 Sixteen healthy male Xinjiang Brown cattle with similar age (18-month-old) and body weight (436.87 kg±17.29 kg) were randomly divided into 2 groups with 8 calves per group.The steam-flaked corn was used in the concentrate of experimental group and the chopped corn was used in control group.A 15-d adaptive phase was followed by 180-d of experimental period.Initial body weight and final body weight were recorded and average daily gain was calculated.The rumen fluid of Xinjiang Brown cattle was collected at 0,1,3,5,7,9 h after feeding on the 180 th day of the experiment to determine the rumen fermentation indexes,and the rumen fluid was collected at 0 h to analyze the composition of rumen microbial flora by 16S rRNA.【Result】 Compared with the control group,the average daily gain was significantly increased (P<0.05),the pH of rumen fluid was significantly decreased at 1 h (P<0.05) and extremely significantly decreased at 3 h (P<0.01), the contents of acetic and acetic+propionic+butyric in rumen fluid were significantly increased (P<0.05),and the content of propionic was significantly increased (P<0.01), ammonia nitrogen and microbial protein in rumen fluid increased significantly at all sampling time points (P<0.01) of the experimental group.There was no significant difference in Chao1 index and Shannon index between the two groups (P<0.05).Compared with the control group, at the phylum level,the relative abundance of Bacteroidetes was significantly increased (P<0.05),and the relative abundance of Spirochaetota was significantly increased (P<0.01),however,the relative abundance of Firmicutes,Desulfobacterota and Verrucomicrobiota decreased significantly (P<0.05),and the relative abundance of Actinobacteriota decreased very significantly (P<0.01) in the experimental group. At the genus level,the relative abundance of Rikenellaceae_RC9_gut_group,Prevotellaceae_UCG-003,Lachnospiraceae_XPB1014_group and Lachnospiraceae_NK3A20_group in the experimental group increased significantly (P<0.05),while the relative abundance of Christensenellaceae_R-7_group decreased significantly (P<0.05).【Conclusion】 The utilization of steam-flaked corn in diet could significantly increase the average daily gain,change the ruminal fermentation speed,improve fermentation efficiency, increase the microbial abundance related to carbohydrate and volatile fatty acid metabolism,and reduce the microbial abundance related to fiber degradation and disease of Xinjiang Brown cattle.

Key words: steam-flaked corn; Xinjiang Brown cattle; volatile fatty acid; rumen microorganism