Gut microbiota in poultry: Roles in nutrition, metabolism and production performance.

The gut microbiota plays an important role in nutrient utilization, intestinal homeostasis, immune regulation, and production performance in poultry. Its composition and functional activity are shaped by complex interactions among host species, developmental stage, intestinal segment, diet, genetic background, and rearing environment. This review summarizes current knowledge of the poultry gut microbiota, with particular emphasis on its roles in nutrition, metabolism, and production performance. We first examine microbial composition and spatial distribution across major poultry species, including broiler chickens, laying hens, ducks, geese, and turkeys, and discuss the factors contributing to interspecies and interstudy variation. We then evaluate how dietary components, including fiber, protein, amino acids, and lipids, modulate microbial communities and metabolic pathways. Particular attention is given to microbial fermentation, short-chain fatty acid production, microbial nitrogen metabolism, bile acid transformation, and host-microbiota signaling, which collectively influence nutrient utilization, intestinal barrier function, immune homeostasis, and metabolic regulation. The potential of microbiota-targeted strategies, including probiotics, prebiotics, synbiotics, dietary fiber manipulation, reduced-protein diets, and emerging microbial interventions, to improve feed efficiency, growth performance, carcass characteristics, meat quality, and resilience to environmental stress is also discussed. In addition, the implications of gut microbiota regulation for nitrogen utilization, ammonia emissions, animal welfare, and antibiotic-free production are considered. Despite substantial progress, the translation of microbiome research into practical applications remains limited by inconsistent experimental designs, methodological heterogeneity, insufficient functional validation, and a lack of causal evidence. Integrating multi-omics approaches with controlled intervention studies and standardized experimental frameworks will be essential for defining causal microbiota-host interactions and developing precision microbiota-based strategies. Overall, a functional understanding of the diet-microbiota-host axis may provide new opportunities to improve poultry productivity, health, and sustainability.