Bacillus subtilis has been widely used in animal husbandry as a potential alternative to antibiotics due to its excellent bacteriostasis and antioxidant activity. This study aims to investigate the effects of Bacillus subtilis on the protection of ducks from Escherichia coli infection and its mechanism. The four experimental groups include the negative control group, positive control group, antibiotic group and Bacillus subtilis group. Ducks in positive, antibiotic and Bacillus subtilis groups are orally administered with Escherichia coli and equivalent saline solution for the negative group. The results show that supplements with Bacillus subtilis enhances the performance and health status of the infected ducks. Moreover, Bacillus subtilis alleviates the increase in globulin, LPS and MDA, and the decrease in albumin, T-AOC and T-SOD in the serum caused by Escherichia coli infection. Bacillus subtilis also attenuates injury in the intestine and partially reverses the increase in ROS production and the depletion of ATP in the jejunum. These effects are accompanied with the change of related genes of the ribosome (13.54%) and oxidative phosphorylation (6.68%). Collectively, Bacillus subtilis alleviates the damage caused by Escherichia coli infection in ducks by activating ribosome and oxidative phosphorylation signaling to regulate antioxidant and energy metabolism.

Peanut meal (PNM) is a byproduct of the peanut oil extraction process, but its application is seriously limited by the presence of anti-nutritional factors, imbalance in amino acid profiles, and susceptibility to mycotoxin contamination. This study was conducted to investigate the effects of solid-state fermentation on the nutritional quality of PNM, as well as the effects of PNM and fermented peanut meal (FPNM) on the ileal digestibility of amino acids and apparent metabolizable energy (AME) of broiler chickens. The results indicated that the fermentation improved the quality of PNM by increasing the crude protein, TCA-soluble protein, and L-lactic acid concentration (p < 0.05), and decreasing the crude fiber, phytic acid, and aflatoxin B₁ concentration (p < 0.05). Solid-state fermentation also increased the free amino acids level and improved the balance of hydrolyzed amino acids of PNM. A nitrogen-free diet was used to determine the loss of endogenous amino acid in birds, and the PNM or FPNM as the only protein source to formulate semi-purified diets. The result showed that feeding on FPNM resulted in higher apparent ileal digestibility (AID) and standardized ileal digestibility (SID) values of the essential amino acids of methionine, lysine, leucine, and phenylalanine (p < 0.05). Moreover, the AID and SID values of the non-essential amino acids of FPNM were both higher than those of PNM, except for proline (p < 0.05). The AME was determined by the classic substitution method, and the results showed that fermentation had no effect on the AME value (p > 0.05). In conclusion, solid-state fermentation improved the nutritional value of PNM, and FPNM was a potential ingredient as an alternative protein source for broilers.