Due to the lack of corn and soybean meal in animal feeding, rice bran meal (RBM) has been proposed as a beneficial substitute for these feedstocks’ ingredients. Its fermentation by using diverse microbes has been adopted as a beneficial technique. In this study, 18 five-month-old finishing pigs (castrated Duroc × Landrace × Large White) were assigned to three dietary groups with six replicates in each group, designated as the control (CON), unfermented RBM (RBM), and fermented RBM (FRBM) groups. RBM was fermented with a mixture of Lactobacillus johnsonii L63 and hydrolytic enzymes at 37 °C and pH 4.8 for 60 h. The results indicated that incorporating 30% fermented or unfermented rice bran meal into the diets of finishing pigs had no significant effect on growth performance. Regarding serum biochemical parameters, most indicators, including alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, and triglycerides, showed no significant alterations. However, in both the unfermented and fermented rice bran meal groups, the concentrations of serum total protein, albumin, globulin, cholesterol, and blood urea nitrogen were significantly decreased (p < 0.05), whereas serum nitric oxide levels were significantly increased (p < 0.05). The FRBM group improved intestinal morphology and the digestibility of nutrients (crude protein, ether extract, crude fiber, and gross energy) by altering the mTORC1 pathway and upregulating the relative expression of amino acid and peptide transporter genes in the jejunum. However, the dry matter digestibility decreased compared to the CON group. The RBM group reduced nutrient digestibility, along with alterations in hepatic gene expression related to amino acid metabolism and transport. Therefore, fermented rice bran meal may offer a potential substitute feed ingredient for use in swine diets when conventional ingredients like corn and soybean meal are in short supply.

Background: The valorization of sustainable feed ingredients such fermented de-oiled rice bran meal (FDRBM) is crucial; however, the molecular mechanisms driving its benefits remain unclear. This study addresses this gap by investigating FDRBM as a dietary substitute for maize in rabbits to determine its effects on meat quality and underlying gut–liver axis communication. Methods: In an eight-week trial, New Zealand White rabbits were assigned to a control diet or the basal diet with a 20% substitution of either unfermented de-oiled rice bran (UFDRBM) or FDRBM. Post-trial, the researchers analyzed carcass traits, meat quality, and nutritional composition. A multi-omics approach integrates gene expression data from the ileum and muscle with liver metabolomics to model coordinated biological responses. Results: Although growth performance was similar, the FDRBM diet significantly improved meat quality by enhancing water-holding capacity and increasing essential amino acids (p < 0.05). Mechanistically, these improvements were associated with the upregulation of genes associated with oxidative muscle fiber (Tnnc1) and lipid metabolism. Analysis of the gut–liver axis revealed that FDRBM enhanced ileum antioxidant capacity, which coincided with profound reprogramming of liver metabolism (p < 0.01 *), identifying C17-sphinganine as a differential metabolite. Conclusion: This study provides novel insights into the mode of action of FDRBM, suggesting that it enhances rabbit meat quality in part by modulating metabolic gene expression and is associated with coordinated molecular changes across the gut–liver axis.