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This study used metatranscriptomics to investigate the effects of concentrate diet level on rumen microbiome composition and function in goats. A total of 12 healthy 120-day-old Da'er goats were randomly allotted into two treatments: L group (low dietary concentrate level group, concentrate: forage ratio was 25: 75) and H group (high dietary concentrate level group, concentrate: forage ratio was 80: 20). The study included a 10-day pre-feeding period and a 60-day growth experiment. The results showed that compared with the L group, the average daily gain and the slaughter rate in the H group were increased, while the F/G was decreased; the concentration of lactate and ammonia nitrogen, and the proportion of butyrate and valerate in the rumen of the H group were increased, while the proportion of acetate, and the ratio of acetate to propionate were decreased ( p  < 0.05). Among rumen bacteria, compared with the L group, the H group significantly decreased the relative abundance of Firmicutes and Fibrobacteria at the phylum level, decreased the relative abundance of Bacteroidetes , Fibrobacter , and Sarcina and increased the relative abundance of Clostridium at the genus level, and decreased the relative abundance of Fibrobacter succinogenes , Sarcina sp. DSM 11001, Oscillibacter sp. KLE 1728, and Ruminococcus flavefaciens and increased the relative abundance of Clostridium sp. ND2 and Firmicutes bacteria CAG: 103 at the species level ( p  < 0.05). Among rumen fungi, the relative abundance of Basidiomycota, Neocallimastigomycota, Mortierella , Mortierella elongata, and Gonapodyna prolifera was lower in the H group than that in the L group ( p  < 0.05). Functional annotation results showed that the abundance of Glycoside hydrolases genes in rumen microbiome was significantly decreased in the H group compared to the L group ( p  < 0.05). The result of KEGG DEGs enrichment analysis showed that the gene expression of cellulose 1,4-β-cellobiosidase, acetyl-CoA hydrolase, lactate dehydrogenase, succinate-semialdehyde dehydrogenase, D-malate dehydrogenase and related genes in methane production pathways of rumen microbiome was decreased in the H group. In summary, feeding high concentrate diets improved the production performance of goats, altered the structure and composition of rumen microbiome and changed the function of rumen microbiome., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Mao, Wang, Wang, Xue, Peng, Hu and Xiao.)