Fermented Liquid Feeding Modulates Intramuscular Fat Deposition and Lipid Composition in Pork: Integrated Metabolomic and Proteomic Insights

Fermented liquid feeding (FLF) has been proposed as a nutritional intervention with the potential to influence pork quality, yet its effects on intramuscular fat deposition and muscle lipid composition remain unclear. In this study, pigs were fed a basal dry feed, liquid feed, or FLF regimen for 173 days, and porcine muscle samples were subsequently evaluated for carcass traits, meat quality, lipid composition, and molecular changes associated with lipid deposition. Compared with CON, FLF reduced average backfat thickness, while intramuscular fat and triglyceride contents in the longissimus thoracis muscle were greater than those in CON and LF (p < 0.05). Fatty-acid profiling showed that FLF increased several major fatty acids, including palmitic acid. Metabolomic analysis identified contrast-specific changes in phosphatidylserine and phosphatidylethanolamine species. Proteomic analysis, together with Western blotting and RT-qPCR, showed higher abundances of PPARγ, FASN, and downstream lipogenic transcripts in the FLF group. These findings demonstrate that FLF modulates lipid deposition and lipid composition in porcine muscle and provide mechanistic insight into the nutritional regulation of pork quality formation.