Gut health as a determinant of nutrient use efficiency in poultry: biological basis and nutritional optimization.

Efficient nutrient use is fundamental to sustainable poultry production because it influences productive performance, feed costs, animal welfare, and environmental nutrient losses. Although improvements in nutrient utilization have traditionally focused on diet formulation and feed additives, increasing evidence demonstrates that gut health is a central biological determinant governing digestion, absorption, and retention of nutrients. Gut health encompasses the coordinated interaction among intestinal morphology, digestive physiology, epithelial barrier integrity, gut microbiota, and mucosal immune homeostasis, all of which collectively regulate nutrient use efficiency. Disruption of these components by nutritional imbalances, enteric pathogens, heat stress, mycotoxins, and management-related stressors impairs digestive and absorptive function, increases intestinal permeability, alters microbial ecology, and redirects nutrients from productive processes toward immune activation and tissue repair. Consequently, maintaining intestinal homeostasis has become a major objective of modern poultry nutrition. This review synthesizes current knowledge on the biological mechanisms linking gut health with nutrient use efficiency and examines how intestinal development, digestive function, nutrient transport, barrier integrity, microbial metabolism, and immune regulation interact to determine productive performance. Major nutritional, environmental, and pathological factors compromising gut function are discussed, together with current nutritional strategies including precision diet formulation, microbiota modulation, feed enzymes, functional amino acids, phytogenic compounds, antioxidants, and trace minerals that improve intestinal function and nutrient utilization. Collectively, the evidence synthesized in this review demonstrates that maintaining gut health is fundamental to maximizing nutrient use efficiency and provides a biological foundation for improving productive efficiency while reducing nutrient losses and supporting more sustainable poultry production.