Bacillus-based probiotics and fermented products as alternatives to antibiotic growth promoters in poultry: Current perspectives

Over the years, antibiotic growth promoters (AGPs) have been prophylactically added to the diet of poultry to enhance growth performance and production traits. Mechanisms of AGP action are still poorly understood. Several hypotheses have been proposed to explain the action of AGPs, including reduction in the subclinical intestinal infections, inhibition of toxin releases by intestinal bacteria, and improvement in the absorption of nutrients. However, overuse of AGPs in poultry production may contribute to the emergence of antibiotic resistance. Therefore, many countries have banned the use of AGPs in animal production, driving scientists to explore suitable and effective alternatives to AGPs for commercial use. Probiotics are a sustainable alternative to AGPs, and Bacillus species have been broadly examined for their ability to prevent pathogenic infections and enhance the growth performance of poultry. Currently, liquid-state fermentation is the main strategy used for the production of Bacillus species. However, because of the cost, sustainability, and feasibility concerns associated with this strategy, solid-state fermentation has been attracting increasing attention. In addition to probiotics, Bacillus-based solid-state-fermented products contain Bacillus-derived secondary metabolites with antibacterial activity. Because the main components of Bacillus-based products produced by liquid-state and solid-state fermentation are different, the performance-promoting mechanism of these products will also be different. This review discusses the latest advancements in the application of Bacillus as an alternative to AGPs for promoting gut health and growth performance in poultry. Feasibility assessment of Bacillus-based solid-state-fermented products as AGP alternative and their mechanism of action is also discussed.