Abstract
Background: To address rising demand for dairy products, dairy goats are often fed high-concentrate diets, which lead to subacute rumen acidosis (SARA). The mechanisms behind individual variation in SARA tolerance are not well understood. This study aims to elucidate roles of rumen microbiome-host interactions in SARA-susceptibility and tolerance. Results: Goats susceptible or tolerant to SARA were selected by feeding diets with different levels of rumen degradable starch. SARA-susceptible goats present prolonged periods of rumen pH below 5.8 and volatile fatty acids (VFAs) accumulation. Metagenomic analysis reveals a decrease in cellulose- and hemicellulose-utilizing bacteria and enzymes, along with increased lysozymes, suggesting disrupted rumen homeostasis. Transcriptomic and single-nucleus transcriptome analyses reveal upregulated Th17 cells, IL-17 signalling, and inflammatory pathways in SARA-susceptible goats. In contrast, SARA-tolerant goats maintain stable pH levels and enhance VFAs absorption. Bifidobacterium adolescentis and other beneficial bacteria are enriched in the rumen of SARA-tolerant goats. These microbes are positively correlated with 3-methyl pyruvic acid, a key metabolite involved in branched-chain amino acid synthesis and epithelial cell proliferation. Both microbiome transplantation and B. adolescentis direct feeding experiments confirm the protective effects of SARA-tolerant microbiota including B. adolescentis, promoting rumen epithelial VFAs absorption and reducing ruminal inflammation. Conclusions: This study highlights the importance of Th17-mediated immune responses in ruminal inflammation and the role of B. adolescentis in regulating rumen epithelial VFAs absorption. Modulating VFAs absorption in the rumen epithelium represents a promising strategy for improving animal health and enhancing rumen fermentation efficiency.