The "Silent Drivers" of Ruminant Vitality: How Bile Acids Link Immunity and Lipid Metabolism
Author：Lachance
Time：2026-01-16
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In recent years, research surrounding the "gut microbiota-bile acids" axis has become a significant focal point. Studies have demonstrated that bile acids possess antibacterial, anti-inflammatory, and signaling functions. They can improve intestinal morphology, maintain barrier integrity and internal homeostasis, and enhance intestinal mucosal immune function, thereby promoting the growth development and production performance of ruminants.The underlying mechanism primarily involves bile acids activating FXR (farnesoid X receptor), which regulates the expression of fibroblast growth factors (FGF). This process inhibits intestinal epithelial damage caused by the over-proliferation of gut microbes while simultaneously increasing the richness of beneficial bacteria, thus improving gastrointestinal health.Furthermore, the intestinal bile acid-TGR5 axis is a key pathway for regulating lipid metabolism. Bile acids, such as lithocholic acid (LCA) and deoxycholic acid (DCA), act as activators for TGR5, stimulating the release of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), which regulate appetite and lipid metabolism. After ruminants ingest a diet, bile acids are secreted from the gallbladder into the digestive tract. Through the dehydroxylation process of gut microbes (such as Firmicutes and Clostridium), primary bile acids are converted into secondary bile acids like DCA and LCA. These enhance the activity of lipolytic enzymes, accelerating the decomposition and absorption of lipids in the diet.Research indicates that microorganisms related to bile acid metabolism exhibit region-specific distribution across different intestinal segments of dairy cows. The contribution of large-intestinal microbiota to bile acids metabolism is particularly significant. Specifically, the concentrations of conjugated bile acids (e.g., taurocholic acid, glycocholic acid, and taurodeoxycholic acid) are highest in the duodenum and jejunum. In contrast, microbe-derived secondary unconjugated bile acids ($\beta$-DCA, LCA, 12-KetoLCA, and isoLCA) are mainly enriched in the large intestine, showing distinct regional tolerance characteristics.Additionally, the genera Prevotella, Roseburia, and Coprococcus in the gut microbiota of Angus cattle show a significant positive correlation with the expression of lipid metabolism genes, promoting intramuscular fat deposition and improving beef quality.Other studies have pointed out that G protein-coupled receptors (GPRs) are key regulators of signaling pathways for lipid deposition. Bile acids and their derivatives can act as signaling molecules by binding to GPRs, influencing the lipid metabolism of gut microbiota and reducing the production of glycerol and fatty acids, thereby improving lipid metabolism under high-fat diets.For instance, increasing the energy and protein levels in the diets of Simmental replacement heifers can significantly enhance gut microbial diversity. This promotes the enrichment of metabolic pathways including protein synthesis, tryptophan metabolism, pyrimidine metabolism, purine metabolism, and taurine/hypotaurine metabolism. Ultimately, this maintains glucose and lipid metabolic homeostasis, improving the body condition and production performance of the heifers.Source: Dong, Y. (2025). Response Characteristics and Mechanisms of Yak Bile Acid Metabolism to Energy Intake Levels [Doctoral dissertation, Lanzhou University]. DOI: 10.27204/d.cnki.glzhu.2025.000992.
