This study investigates the effect of walnut green husk extract (WE) on gut microbiota, metabolites, and immune-antioxidant changes in fattening pigs through gut microbiota-metabolite interactions. A total of 60 healthy fattening pigs (Duroc × Landrace × Yorkshire) with an initial body weight of 65.2 ± 3.1 kg were randomly assigned to two groups (n = 30 per group): the control group (NC), which was fed a basal diet, and the WE group, which was fed the basal diet supplemented with 0.1% walnut green husk extract (WE). Dietary supplementation with 0.1% WE significantly increased the relative abundances of beneficial bacteria (e.g., Firmicutes, Lactobacillus) and reduced pathogenic bacteria (e.g., Proteobacteria, Shigella). Untargeted metabolomics identified 170 differentially accumulated metabolites, among which propionic acid—a key short-chain fatty acid with immunomodulatory effects—was significantly upregulated by 1.09-fold (p = 0.03) and showed a positive correlation with beneficial microbial abundances. These metabolites were enriched in glycerophospholipid and α-linolenic acid metabolism pathways, where eicosadienoic acid inhibited the nuclear factor kappa-B (NF-κB) pathway for anti-inflammatory effects, and methyl cinnamate synergistically regulated mitogen-activated protein kinase (MAPK) signaling with Lactobacillus. Serum analyses showed that WE significantly enhanced IgA, IgM, and IgG levels by 3.97-fold, 4.67-fold, and 4.43-fold (p < 0.01), reduced malondialdehyde (MDA) concentration by 82.8% (p < 0.01), and trended to improve antioxidant capacity via glutamine. Mechanistically, WE promoted short-chain fatty acid production by beneficial bacteria, forming a “microbiota–metabolite–immunity” cascade to enhance lipid metabolism and alleviate intestinal inflammation. These findings highlight that WE provides multi-omics evidence for its application as a functional feed additive.

To investigate the molecular mechanisms underlying muscle fiber development in different pig breeds and their impact on meat quality, this study collected the longissimus dorsi muscle of the indigenous Huainan pig and the commercial Large White pig at four developmental stages (0, 7, 14, and 21 days postnatal). Muscle fiber types were identified using myosin ATPase staining, while transcriptomics and non-targeted metabolomics were employed to analyze differences in gene expression and metabolite composition. The results showed that the Huainan pig had a higher proportion of oxidative muscle fibers, indicating superior aerobic metabolic capacity and meat quality. Transcriptome data identified 18 differentially expressed genes common to both pig breeds, including KLF4, NOS1, SH3KBP1, and TRARG1, which were upregulated in Huainan pigs to regulate muscle fiber type composition and meat quality by influencing mitochondrial function, nitric oxide synthesis, and glucose/lipid metabolism. Metabolomics analysis revealed significantly elevated levels of carnosine, citrulline, serine, and glycerol-3-phosphate in Huainan pigs, which are associated with metabolic pathways promoting muscle fiber transformation via enhancing energy supply, antioxidant capacity, and fatty acid oxidation. Notably, integrated transcriptome–metabolome analysis showed that oxidative metabolism genes (e.g., KLF4) and metabolites (e.g., citrulline) formed an AMPK-mediated ‘gene–metabolite’ loop in Huainan pigs, which synergistically promotes mitochondrial function and fiber differentiation. In summary, this study provides new insights into the molecular mechanisms underlying meat quality differences between pig breeds and offers a theoretical basis for the breeding and development of high-quality pork.