The yak is an iconic ruminant of the Qinghai-Tibet Plateau, yet segment-specific variation in its intestinal microbial functional potential and bile acid profiles under different feeding systems remains insufficiently characterized. Six healthy adult male yaks with similar body weights (320 ± 30 kg) were assigned to grazing (G) or stall-feeding (S) systems, with three animals per group, for a 90-day trial comprising a 10-day adaptation period and an 80-day formal experimental period. The individual yak was considered the experimental unit, and intestinal segments sampled from the same animal were treated as repeated observations. Liver tissue and digesta from the duodenum, ileum, cecum, and colon were analyzed using targeted bile acid metabolomics and shotgun metagenomics. Principal coordinate analysis based on Bray-Curtis dissimilarities showed segment-associated clustering of microbial communities, with PCo1 and PCo2 explaining 65.5% and 18.9% of the total variation, respectively. ANOSIM identified a significant intestinal-segment effect on microbial community composition (R = 0.2208, BH-FDR = 0.0144), whereas the overall feeding-system effect was not significant (R = 0.3747, BH-FDR = 0.1200). No statistically significant feeding-system differences were detected in Shannon, Simpson, Chao1, or ACE indices within individual intestinal segments (BH-FDR ≥ 0.800), and PERMDISP detected no significant differences in within-group dispersion (BH-FDR ≥ 0.1682). Bacillota and Bacteroidota were the dominant phyla. Descriptive functional profiling showed higher mean ileal abundances of GH2 (0.0035 vs. 0.0026), GH3 (0.0029 vs. 0.0024), and GH43 (0.0021 vs. 0.0013) in grazing yaks, whereas the starch-associated GH13 family showed its highest mean abundance in the colon of stall-fed yaks. These metagenomic patterns represent predicted genomic functional potential rather than gene expression, enzyme activity, or metabolic flux. Cecal total bile acid concentration showed a nominal between-group difference (unadjusted Welch’s p = 0.0109), but this difference did not remain significant after correction across the five anatomical sites (BH-FDR = 0.0545). In the colon, stall-fed yaks had a lower conjugated-to-unconjugated bile acid ratio and a higher secondary-to-primary bile acid ratio than grazing yaks (BH-FDR < 0.05). Feeding-system-associated descriptive patterns were observed in predicted microbial functional profiles, whereas statistically supported between-group differences were limited mainly to selected colonic bile acid ratios. Given the limited animal-level replication, these findings should be considered exploratory.

Hypobaric hypoxia poses a serious threat to growth and development and can induce pronounced inflammatory responses. These effects are closely associated with the gut microbiota. However, the underlying mechanisms, particularly the role of gut microbiota in regulating hepatic metabolism under chronic hypoxic conditions, remain poorly understood. In this study, SD rats were used as recipients and assigned to three groups: a hypobaric hypoxia group (H), an antibiotic-treated group (HA), and an antibiotic-treated group receiving fecal microbiota transplantation from plateau zokors (HAM). All rats were maintained in a hypobaric hypoxia chamber simulating an altitude of 6000 m for 30 days. Subsequently, growth performance, routine hematological parameters, and multi-omics profiles were evaluated. Compared with the H group, both the HAM and HA groups showed significantly increased average daily gain (ADG) (p < 0.05), while the ADG/ADFI ratio was significantly higher in the HAM group than in the H group (p < 0.05). Monocyte count (Mon#) and monocyte percentage (Mon%) were significantly higher in the HA group than in both the H and HAM groups (p < 0.05). Microbiota analysis revealed significant enrichment of Lachnospiraceae_NK4A136_group in the HAM group, whereas Desulfovibrio was significantly enriched in the HA group (p < 0.05). Fecal metabolomics showed that ursodeoxycholic acid (UDCA) was significantly increased in the HAM group (p < 0.05). In the liver metabolome, the anti-inflammatory lipid FAHFA 18:1/20:3 was significantly elevated in the HAM group, whereas pro-inflammatory factors, including uric acid and leukotriene D4, were significantly reduced (p < 0.05). Correlation analysis further demonstrated that the abundance of Lachnospiraceae was positively correlated with FAHFA 18:1/20:3 and negatively correlated with uric acid and creatinine (p < 0.05). Collectively, these findings indicate that the gut microbiota can modulate gut–liver metabolism, alleviate inflammatory responses, and enhance the adaptation of rats to hypoxic environments. This study provides valuable insights into potential strategies for promoting sustainable animal health and adaptation under hypoxic conditions.

This study investigated the effects of three roughage physically effective neutral detergent fiber (peNDF_8.00) levels (11.52%, 13.16%, and 15.43% on an as-fed roughage basis) on growth performance, rumen fermentation, serum biochemical parameters, rumen microbiota, and rumen metabolomic profiles in yaks. Thirty healthy yaks were allocated to three treatment groups (A, B, and C). The roughage peNDF_8.00 treatments did not significantly affect short-term growth performance. Ruminal valerate concentration was significantly higher in group C than in group A (p < 0.05), while the molar proportions of isobutyrate and isovalerate differed significantly among treatments (p < 0.001). Serum aspartate aminotransferase (AST) activity and blood urea nitrogen (BUN) concentration also differed significantly among treatments (p < 0.05). Rumen microbiota analysis revealed treatment-associated differences in Chao1 richness and variation in microbial community structure, while LEfSe identified Bacteroidota and Xylanibacter as exploratory candidate biomarkers of group C. PICRUSt2 analysis suggested treatment-associated variation in predicted microbial functional potential. Untargeted metabolomics identified multiple candidate treatment-associated metabolic features; however, no KEGG pathway remained significant after Benjamini–Hochberg false discovery rate (FDR) correction. Overall, higher roughage peNDF_8.00 was associated with variation in rumen fermentation, microbial community structure, and metabolomic profiles, without a detectable effect on short-term growth performance.