Multi-omics identifies microbial and miRNA biomarkers from rumen fluid for susceptibility of subacute ruminal acidosis in dairy goats.

With the increasing intensification of animal husbandry, high-concentrate diets are often used in production to ensure high production performance in dairy animals, leading to susceptibility to subacute rumen acidosis (SARA), yet reliable early diagnostic biomarkers remain lacking. In this study, a high-RDS diet was fed to dairy goats as a model, and SARA-tolerant and SARA-susceptible individuals were identified under this diet. By combining 16S rRNA gene sequencing, metagenomic binning, and miRNA transcriptome sequencing, the changes in rumen microbial composition, function, and miRNAs in dairy goats after SARA onset were analyzed, with the goal of screening for potential diagnostic targets. Analysis of rumen fermentation parameters showed that, compared with the CON, the SARA group had significantly higher butyrate and total VFAs, together with increasing trends in acetate, propionate, isobutyrate, and valerate. Compared with CON, SARA and SARA-T goats showed increased NH3-N concentration, whereas the abundance of rumen microbes such as Prevotella, which is involved in cellulose degradation, significantly decreased. Compared with CON and SARA-T, the microbial functions of SARA shifted toward energy acquisition pathways. The miRNA analysis revealed that Compared with CON, the differentially upregulated miRNAs in the SARA group target immune-related genes such as IL-12RB. Comparing SARA with SARA-T revealed that differentially expressed miRNAs were enriched in the TNF signaling pathway. By integrating random forest and ROC analyses, a combined "microbe-miRNA" signature comprising the low-abundance genus Ruminobacter, the miRNA 7_14677, and chi-miR-361-5p was identified. This signature exhibited high diagnostic accuracy not only between CON and SARA but also between SARA and SARA-T, as well as between pooled healthy (CON+SARA-T) and SARA animals.