The fermented feed used in broiler production has gained significant attention for its potential to improve growth performance, enhance gut health, and modulate gut microbiota. This review synthesized findings on the effects of both solid and liquid fermented feed in broilers. Fermentation processes enhance nutrient bioavailability; reduce anti-nutritional factors; and generate beneficial metabolites, such as short-chain fatty acids, which contribute to gut health. Incorporating fermented feed in broiler diets has been shown to improve weight gain, the feed conversion ratio, and nutrient absorption by promoting favorable gut morphology changes, including an increased villus height and villus height-to-crypt depth ratios. Additionally, fermented feed fosters a beneficial microbial environment by increasing lactic acid bacteria populations while reducing pathogenic microbes. Fermentation also modulates gut immunity by regulating cytokine production and stimulating immune cell activity. However, challenges such as inconsistent effects on feed intake and growth during the early production stages underscore the need for optimizing fermentation protocols tailored to broiler production systems. Although the implementation of liquid fermented feed presents logistical challenges, research suggests it can significantly improve feed digestibility. Advances in precision fermentation techniques and multi-strain inoculant use hold promise for further improving fermented feed efficacy. Future research should focus on assessing the long-term impacts, economic viability, and environmental sustainability of fermented feed in commercial poultry systems. Overall, fermented feed offers a promising strategy to enhance productivity and sustainability in broiler farming while reducing the reliance on conventional feed additives. This review reflects the body of knowledge at the time of writing.

Feed accounts for up to 80% of poultry production costs, with high-quality grains such as soybean meal and corn traditionally serving as primary ingredients. However, increasing costs and competition for these grains have driven interest in low-grade and unconventional feed ingredients, including by-products like rapeseed meal and cottonseed meal. These alternatives are often constrained by high fiber content, anti-nutritional factors, and reduced nutrient bioavailability. Fermentation has emerged as a promising strategy to address these limitations, enhancing digestibility, palatability, and antioxidant properties while degrading harmful compounds such as tannins, trypsin inhibitors, and free gossypol. Solid- and liquid-state fermentation techniques utilize microbial inoculants, including lactobacilli and Bacillus species, to enzymatically break down complex macromolecules, thereby releasing essential nutrients. When combined with pretreatments like enzymatic hydrolysis, fermentation significantly improves the nutritional quality of feed ingredients while reducing costs without compromising poultry health or performance. This review examines the mechanisms, benefits, and challenges of fermentation techniques in poultry feed production, underscoring the importance of further research to optimize fermentation parameters, identify novel microbial strains, and ensure scalability and safety in industrial applications.