Lactobacillus fermentum supplementation modulates jejunal microbiota, metabolome, and morphology in yaks under high-energy feeding

Concentrated supplementary feeding is an effective strategy for addressing nutritional deficiencies in yaks during the cold-season grazing period. However, limited research has investigated whether long-term implementation may alter the gut microbiota and metabolite profiles of yaks, potentially posing health risks to the host. This study investigated the regulatory role of Lactobacillus fermentum in host metabolism through the gut microbiota, employing a “nutrition-gut-metabolism” perspective. Eighty healthy male Pamir yaks with similar body conditions were randomly divided into four groups (n = 20 per group), including Control (Con), Medium Energy (ME), High Energy (HE), and Medium Energy plus Lactobacillus fermentum (MEJ). Body weight was recorded every 30 days during the 150-day trial. Jejunal tissues and contents from nine yaks per group were collected for subsequent analyses. Key findings revealed that the HE group showed significantly increased crypt depth and elevated relative abundance of Clostridium_sensu_stricto_1 (P < 0.05). In contrast, the MEJ group reversed the decline in villus height and width observed in the ME group, while significantly enhancing muscularis thickness. Notably, MEJ yaks exhibited higher abundance of Paeniclostridium, Romboutsia and Treponema (P < 0.05) and markedly increased short-chain fatty acids concentrations (P < 0.001). Metabolomic analysis identified upregulated pathways, including D-amino acid metabolism and Neuroactive ligand-receptor interaction. Furthermore, comparative analyses pinpointed five critical microbial taxa (e.g., vadinBE97, Lachnospiraceae_UCG-008) and 18 key metabolites (e.g., 15-Deoxyprostaglandin J2, Lasalocid A) associated with these effects. In conclusion, Lactobacillus fermentum supplementation improved yak growth performance and mitigates metabolic risks linked to excessive energy intake. These findings provided a theoretical foundation for optimizing yak feeding strategies and advancing precision nutrition in ruminant production.