Integrated gut metagenomic and muscle proteomic analysis reveals the role of dietary fermented extruded brewers' spent grain in enhancing pork quality through the gut-muscle axis

<h4>Background</h4>The fact that feeding pigs with probiotic-fermented agricultural by-products improves pork quality has been repeatedly demonstrated and widely applied, but the underlying mechanisms remain unclear. This study explored the effects of fermented extruded brewers' spent grain (FEBSG) on meat quality in growing-finishing pigs, as well as its regulatory mechanisms.<h4>Methods</h4>Sixty Duroc × Landrace × Yorkshire pigs (52.25 ± 2.10 kg) were randomly assigned to five dietary treatments, in which FEBSG replaced 0, 5%, 10%, 15%, and 20% of soybean meal (SBM). The experiment spanned 10 weeks.<h4>Results</h4>Compared with the control, 20% FEBSG significantly increased final body weight, average daily feed intake, and average daily gain, while decreasing feed to gain ratio (P < 0.05). Both 15% and 20% FEBSG improved carcass characteristics and meat quality, including higher carcass weight, loin eye area, and intramuscular fat content, along with lower drip loss and shear force (P < 0.05). These treatments also enhanced flavor-related amino acids and unsaturated fatty acids (P < 0.05), and improved umami and sweet taste profiles. Moreover, 20% FEBSG increased muscle fiber density and reduced fiber diameter, upregulated MyHC I, MyHC IIa, PGC-1α, AMPKα1, TFAM, and SDH activity, and downregulated MyHC IIb and LDH activity (P < 0.05). Proteomic analysis identified 69 differentially expressed proteins, with enrichment in AMPK and PPAR signaling pathways. Metagenomic analysis revealed increased abundance of short-chain fatty acid-producing bacteria, including Clostridium, Lactobacillus, Prevotella, and Bartonella. Correlation analysis demonstrated associations between gut microbiota diversity and meat quality traits, as well as between dominant microbial genera and differentially expressed proteins, volatile fatty acids, muscle fiber characteristics, and the AMPK/PGC-1α/TFAM signaling pathway.<h4>Conclusions</h4>Partial replacement of SBM with FEBSG positively influenced growth performance and pork quality in pigs, with the underlying mechanisms may involve the activation of the AMPK/PGC-1α/TFAM signaling pathway via the gut-muscle axis, thereby enhancing mitochondrial biogenesis, muscle development, and metabolism.