Bile acids play a dual role by aiding lipid absorption and acting as signaling molecules by interacting with various receptors. Bile acids are perpetually recycled via enterohepatic circulation and are biotransformation by gut microbiota, making bile acid metabolism a critical regulator of intestinal homeostasis. The intestinal epithelium prominently expresses two key bile acid receptors - the farnesoid X receptor (FXR) and G protein-coupled bile acid receptor 1 (TGR5) - which play indispensable roles in maintaining bile acid homeostasis and intestinal barrier function. Due to the abundant expression of bile acid receptors and the importance of the intestine in preventing pathogen invasion, researchers are increasingly focused on the function of bile acids in this system. This article focuses on the effect of bile acids and their receptors, FXR and the TGR5, in modulating intestinal barrier function.

Growth stage is a key factor influencing the composition and richness of the porcine gut microbiota. The stage-specific alterations in gut microbiota of indigenous Chinese pig breeds and cultivated breeds remain to be elucidated. This study conducted 16S rRNA sequencing analysis on fecal microbiota from Dahe black pigs across distinct growth stages. Samples included lactating sows, suckling piglets, weaned piglets, pigs weighing 50–100 kg, pigs weighing 120–150 kg, and pigs weighing > 200 kg. The results indicated that Escherichia shigella (12.4% vs. 16.2%), Lactobacillus (5.9% vs. 6.3%), and Rikenellaceae RC9 gut group (3.9% vs. 4.2%) were dominant genera shared between lactating sows and suckling piglets. The relative abundance of Eubacterium brachy group was significantly higher in lactating sows, whereas Flavonifractor was significantly lower compared to suckling piglets (p < 0.05). Compared to pigs weighing > 120 kg, lactating sows exhibited 22 differentially abundant genera, including Escherichia shigella, Cloacibacillus, Fusobacterium, Faecalibacterium, and Prevotella (p < 0.05). In suckling piglets, Firmicutes and Bacteroidota constituted 47.4% and 27.3% of the microbiota, respectively. Their relative abundance increased with body weight, reaching 52.6% and 33.3% in pigs weighing > 200 kg. Proteobacteria decreased from 17.3% in suckling piglets to 2.0% in >200 kg pigs. Spirochaetota declined from 2.5% in suckling piglets to 0.9% in weaned piglets and then increased to 6.9% in >200 kg pigs. Lactobacillus peaked at 15.7% in weaned piglets, while Escherichia shigella reached its maximum (16.2%) in suckling piglets, both gradually declining thereafter. Streptococcus abundance remained relatively stable (1.1% in suckling piglets; 4.5% in weaned piglets). Prevotellaceae NK3B31 group registered 2.9% in suckling piglets, increased to 7.1% in weaned piglets, and then declined to 2.6% in >200 kg pigs. Mitsuokella, Bilophila, Succinivibrio, Romboutsia, and Desulfovibrio were identified as the top five genera discriminating suckling and weaned piglets. Similarly, Lachnospiraceae XPB1014 group, Clostridium sensu stricto 1, Turicibacter, Quinella, and p 1088 a5 gut group were key discriminators between weaned piglets and 50–100 kg pigs. These identified microbial taxa represent potential candidate targets for modulating the developmental timing of growth phases in pigs, offering possibilities for either advancing or delaying specific physiological timepoints.

The intestinal immune barrier is a developed and complex immune system, and there is a fine synergy between it and the induced immune response. Short-chain fatty acids (SCFAs) are the main metabolites of intestinal microbial fermentation. In the cecum of pigs, SCFAs not only provide energy for the host but also participate in regulating the function of the intestinal immune system. The purpose of this study was to explore the mechanism of SCFAs in the regulation of immune gene expression in porcine cecum. SCFAs content and mRNA expression levels of immune genes in cecum were detected, and Gene Ontology (GO) function annotation, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, Protein-Protein Interaction Networks (PPI) network construction, key gene identification, and correlation analysis were performed. The results showed that the content of SCFAs in the cecum of Dahe black pigs (DHB) was lower than that of Dahe pigs (DH). There were significant differences in mRNA expression of some immune genes between the two groups. GO functional annotation found terms related to cytokine activity and protein heterodimerization activity; the KEGG pathway was enriched in several pathways related to intestinal immunity. The PPI network identified Interleukin-6 (IL-6), Interleukin-8 (IL-8), Interleukin-10 (IL-10), Interleukin-17A (IL-17A), and Interleukin-18 (IL-18) as key proteins. The correlation analysis showed that acetic acid and valerate were closely related to the immune response. In this study, the differences in cecal short-chain fatty acids and the immune barrier between Dahe pigs and Dahe black pigs were compared, which provided a theoretical basis for improving the intestinal immunity of pigs.

Sepsis is associated with dysregulated bile acid profiles, gut microbiota dysbiosis, and impaired intestinal barrier function. This study investigated the preventive effects and underlying mechanisms of taurocholic acid (TCA) against lipopolysaccharide (LPS)-induced systemic acute inflammation in mice using hematoxylin-eosin (HE), periodic acid-Schiff (PAS), qPCR, ELISA kits, 16S rRNA sequencing and GC-MS. TCA pretreatment (20 mg/kg TCA, TL20; 40 mg/kg TCA, TL40; 60 mg/kg TCA, TL60) mitigated the exacerbation of LPS-induced damage to physical, chemical, and immune barrier functions in the ileum and colon. The TL60 group showed significantly increased mRNA expression of ileal and colonic ZO-1, ZO-2, Claudin-1, Occludin, SC, J chain, CD40, PIgR, and IgA and protein expression of IgA, SIgA, IgG, and IgM in comparison with LCG group (p < 0.05). Notably, TCA upregulated mRNA expression of FXR and TGR5, while suppressing the NF-κB pathway, suggesting a potential anti-inflammatory mechanism. Hepatic concentrations of TCA and taurohyocholic acid (THCA) were significantly lower in the LCG group than in the CG group but elevated in the colon; TCA pretreatment effectively prevented the abnormal accumulation of TCA and THCA in the colon (p < 0.05). Furthermore, TCA pretreatment significantly increased the relative abundance of bile acid-metabolizing genera in the colonic microbiota, including Desulfovibrio, Lactobacillus, Faecalibaculum, Bifidobacterium, Turicibacter, and Anaerostipes. These findings demonstrated that TCA pretreatment alleviates LPS-induced intestinal barrier injury and inflammatory responses by preventing intestinal barrier dysfunction, reducing bile acid retention, and modulating colonic microbial composition.

To mitigate antimicrobial resistance and drug residues, the use of growth-promoting antibiotics in livestock has been prohibited, prompting interest in safe natural alternatives. Lanping black-boned sheep, an indigenous high-altitude breed in Yunnan, exhibit unique physiological traits but relatively low feed efficiency. This study evaluated the effects of three natural additives—guanidinoacetic acid (GAA, 1 g/sheep/day), Ampelopsis grossedentata flavonoids (AGF, 1 g/sheep/day), and 5,6-dimethylbenzimidazole plus cobalt (5,6-DMB + Co; 100 mg 5,6-DMB + 0.5 mg Co/sheep/day)—on serum biochemistry and rumen microbiota in twenty-four Lanping black-boned sheep fed under grazing conditions for 90 days following a 10-day adaptation period. GAA and 5,6-DMB + Co increased serum globulin (p < 0.05), whereas AGF reduced urea concentrations (p < 0.05). Only GAA decreased ruminal pH (p < 0.05). All additives enhanced microbial richness (p < 0.05), with 5,6-DMB + Co inducing the most pronounced community restructuring. Taxonomically, AGF and 5,6-DMB + Co decreased Firmicutes and enriched Verrucomicrobiota, while AGF uniquely increased Cyanobacteria. GAA selectively reduced Quinella, AGF decreased Christensenellaceae_R-7_group and NK4A214_group, and 5,6-DMB + Co markedly enriched Rikenellaceae_RC9_gut_group (p < 0.05). Microbial shifts were closely associated with biochemical indices, including positive associations of Prevotella with AST and Rikenellaceae_RC9_gut_group with total protein (p < 0.05). Overall, GAA mainly affected protein-related indices, AGF lowered serum urea, and 5,6-DMB + Co increased within-sample diversity with accompanying community reweighting, providing a theoretical basis for developing sustainable feeding strategies to enhance both productivity and health in Lanping black-boned sheep.

Yucca schidigera extract (YSE) is a plant-derived feed additive rich in steroidal saponins, polyphenols, and polysaccharides, with demonstrated anti-inflammatory, antioxidant, antibacterial, and ammonia-binding properties. This review systematically synthesizes the major bioactive components, core mechanisms of action, including modulation of the Nrf2/ARE and NF-κB pathways, regulation of ruminal fermentation and ammonia-nitrogen metabolism, and maintenance of intestinal barrier integrity, and the species-specific application effects of YSE in pigs, poultry, ruminants, and aquatic animals. Most studies have shown that YSE can improve growth performance, reproductive efficiency, and product quality while concurrently reducing ammonia and methane emissions. However, the magnitude and consistency of these benefits vary considerably across species, dosage, and experimental conditions, with most evidence derived from controlled trials rather than commercial-scale validation. By integrating cross-species dose–response data and identifying critical knowledge gaps, including product standardization, long-term safety, and economic feasibility under commercial conditions, this review provides a theoretical and practical foundation for the evidence-based application of YSE as a sustainable feed additive. In the context of global efforts to reduce antibiotic use and mitigate environmental pollution from livestock production, YSE represents a promising, multifunctional tool for advancing ecological and low-carbon animal husbandry.