Abstract: Fermented liquid feed (FLF) has emerged as a pivotal technology in sustainable animal husbandry due to its unique microbial metabolic properties and nutritional regulatory functions. FLF was prepared by mixing feed ingredients with water (ratio of 1∶1.5 to 1∶4) and utilizing the synergistic fermentation of probiotics such as lactic acid bacteria and yeasts. Degradation of large molecular proteins and polysaccharides into small molecular active peptides, functional poligosaccharides and short-chain fatty acids, etc., which significantly improved the bioavailability of feed. The low-pH environment of FLF inhibited pathogenic bacteria proliferation while modulating gut microbiota composition, strengthening intestinal barrier function, and optimizing nutrient metabolism. These mechanisms contributed to significant improvements in swine growth performance, gut health, and meat quality. This review systematically summarized the metabolic characteristics of lactic acid bacteria fermentation and the synergistic mechanisms of microbial-enzymatic interactions in FLF, with a focus on its regulatory effects on swine production performance, gut microbiota, and muscle quality. The findings provided theoretical support for the large-scale application of FLF and sustainable development of animal husbandry.

Key words: pig, fermented liquid feed, fermentation mechanism, Nutritional regulation, growth performance, gut health, meat quality