Abstract
Simple Summary The presence of anti-nutritional factors (ANFs) in soybean meal (SBM) is considered the main question that motivates the poultry feed industry to develop its traditional processing techniques. Phytate and trypsin inhibitors are the prominent ANFs in SBM that inhibit nutrient digestion and absorption. One of the most recent and effective processing methods is fermentation of SBM with different fermentative microorganisms. Applying double stages of microbial fermentation of SBM, utilizing Asperigillus oryzae and Bacillus subtilis, was proven to be a highly effective method in eradication of most ANFs, such as phytate and trypsin inhibitors, while simultaneously improving SBM protein and amino acid content. Inclusion of double-fermented soybean meal (DFSBM) in broiler rations triggered better feed efficiency, nutrient digestibility, and amino acid transporters that improved the birds' weight gain and muscle nutritional value. Inclusion of microbial fermented soybean meal in broiler feed has induced advantageous outcomes for their performance and gastrointestinal health via exhibiting probiotic effects. In this study, soybean meal (SBM) was subjected to double-stage microbial fermentation utilizing functional metabolites of fungi and bacteria. In broiler diet, DFSBM replaced SBM by 0, 25, 50 and 100%. DFSBM was reported to have higher protein content and total essential, nonessential and free amino acids (increased by 3.67%, 12.81%, 10.10% and 5.88-fold, respectively, compared to SBM). Notably, phytase activity and lactic acid bacteria increased, while fiber, lipid and trypsin inhibitor contents were decreased by 14.05%, 38.24% and 72.80%, respectively, in a diet containing 100% DFSBM, compared to SBM. Improved growth performance and apparent nutrient digestibility, including phosphorus and calcium, and pancreatic digestive enzyme activities were observed in groups fed higher DFSBM levels. In addition, higher inclusion levels of DFSBM increased blood immune response (IgG, IgM, nitric oxide and lysozyme levels) and liver antioxidant status. Jejunal amino acids- and peptide transporter-encoding genes (LAT1, CAT-1, CAT-2, PepT-1 and PepT-2) were upregulated with increasing levels of DFSBM in the ration. Breast muscle crude protein, calcium and phosphorus retention were increased, especially at higher inclusion levels of DFSBM. Coliform bacteria load was significantly reduced, while lactic acid bacteria count in broiler intestines was increased with higher dietary levels of DFSBM. In conclusion, replacement of SBM with DFSBM positively impacted broiler chicken feed utilization and boosted chickens' amino acid transportation, in addition to improving the nutritional value of their breast meat.