Rumen microbiota and fermentation parameters in Tibetan semi-fine wool sheep reflect growth stages and potential nutritional adaptations

OBJECTIVE: The rumen microbiota plays a pivotal role in fermenting plant biomass, which is essential for nutrient conversion. Although extensive research has examined the intestinal microbiome of Tibetan livestock, the rumen microbiota of semi-fine wool sheep (SF-sheep) remains poorly characterized. This study aimed to profile age-related changes in the rumen microbiota and fermentation parameters of SF-sheep to uncover potential microbial-mediated adaptations to different growth stages. METHODS: Full-grazing male SF-sheep were randomly assigned into three age groups: two-month- old lambs, yearling sub-adults, and approximately 50-month-old adults. 16S rRNA gene sequencing and high-performance liquid chromatography were used to analyze the rumen microbiota composition and short-chain volatile fatty acids (SCVFAs). RESULTS: Age-dependent differences were observed in ruminal NH3-N concentrations, with sub-adult sheep exhibiting higher levels than young and adult individuals, whereas SCVFAs concentrations remained relatively stable. With age, the rumen microbial community structure tended to become more homogeneous, whereas microbial diversity and complexity showed a marked increase during adulthood. At the phylum level, Saccharibacteria and Succiniclasticum were enriched in sub-adults, whereas Euryarchaeota and Prevotellace_UCG_001 were more abundant in adults; no microbial biomarkers were detected in young sheep. Correlation analyses indicated that age and NH3-N concentrations were the primary factors shaping the rumen microbiota. SCVFAs, including acetate, butyrate, and propionate, were positively associated with fibrolytic and polysaccharide-degrading bacteria such as Prevotella_1, Treponema_2, and Selenomonas_1. The rumen microbial communities were classified into two enterotypes. Enterotype 1, predominantly observed in young SF-sheep, showed higher abundances of Kyoto Encyclopedia of Genes and Genomes Orthologs (e.g., K00656, K00239, K01966) associated with acetate, propionate, and butyrate synthesis. CONCLUSION: The rumen microbial ecosystem of SF-sheep showed pronounced age-dependent restructuring in microbial composition and diversity, accompanied by nitrogen metabolism. These changes represent dynamic microbial adaptation to the host's physiological state and potential developmental shifts in nutrient requirements, offering valuable insights for age-specific nutritional management strategies.