Integrated rumen microbiome and lipidomic analyses reveal the effects of feeding-regimes on fat deposition and mutton odor formation in Bashbay sheep.

Abstract

This study investigated how natural grazing and concentrate-based feeding regime regulate mutton odor-related compound deposition through the rumen microbiota-fermentation-lipid metabolism axis in Bashbay sheep. Sixteen healthy 6-month-old uncastrated Bashbay rams were assigned to the natural grazing group (FM) and the concentrate-based feeding group (SS), with eight animals per group. Mutton odor-related compounds, rumen fermentation parameters, rumen microbiota, and lipidomic profiles of subcutaneous adipose tissue (SAT), perirenal adipose tissue (PAT), and tail fat tissue (TFT) were analyzed using gas chromatography-mass spectrometry (GC-MS), full-length 16S rRNA gene sequencing, and untargeted lipidomics. The results showed that, among the three adipose depots, SAT contained the highest concentrations of 4-methyloctanoic acid (MOA), 4-ethyloctanoic acid (EOA), and 4-methylnonanoic acid (MNA), and the overall deposition of mutton odor-related branched-chain fatty acids followed the order SAT > TFT > PAT. Compared with the FM group, SS group significantly increased MNA levels and was associated with higher ruminal isobutyrate concentration and greater relative abundance of Selenomonas, whereas FM group was associated with enrichment of Saccharofermentans. Lipidomic analysis identified 2592 lipid species, mainly triglycerides (TG) and glycerophospholipids (GP). Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) abundance were higher in the FM group, whereas SS group promoted TG accumulation, indicating marked remodeling of adipose tissue lipid composition in Bashbay sheep under different feeding regimes. Notably, PC 37:5 was identified as a shared exploratory candidate biomarker across SAT, PAT, and TFT, suggesting that it may reflect phospholipid remodeling characteristics in adipose tissues under natural grazing and concentrate-based feeding conditions. Partial Spearman correlation analysis showed that, after controlling for feeding regime, the associations between PC 37:5 and rumen fermentation parameters, differential microbial taxa, and mutton odor-related branched-chain fatty acids were no longer significant, indicating that PC 37:5 may be more appropriately interpreted as a candidate lipid marker. In conclusion, FM group and SS group were closely associated with differences in rumen fermentation characteristics, microbial composition, adipose tissue lipid profiles, and the deposition of mutton odor-related branched-chain fatty acids in Bashbay sheep. The lower MNA deposition under natural grazing conditions, together with changes in membrane-related phospholipid composition, suggests that natural grazing may influence mutton odor-related characteristics. This study provides insight into the formation of mutton odor-related compounds in Bashbay sheep under different feeding regimes from the perspective of the "rumen microbiota-fermentation metabolism-lipid remodeling-mutton odor-related precursor deposition" axis.