Part 2: precision nutrition targeting the gut barrier–nutrient transporter interface under heat stress in poultry

SUMMARYHeat stress (HS) compromises intestinal integrity and nutrient utilisation in poultry, but it remains unclear how nutritional interventions directly restore nutrient transporter function. Building on the mechanistic framework established in Part 1, this review evaluates precision nutritional strategies at two levels: foundational diet formulation (energy, digestible amino acids and dietary electrolyte balance) and functional supplementation (vitamins, trace minerals, phytogenics, microbiota-directed additives, organic acids, medium-chain fatty acids, β-glucans and betaine). Particular emphasis is placed on evidence linking these interventions to intestinal nutrient transporters rather than on repeating HS injury pathways. Trace minerals, antioxidant vitamins, microbiota-directed interventions, organic acids, medium-chain fatty acids, phytogenic compounds, β-glucans and betaine can mitigate heat stress–induced intestinal dysfunction through complementary mechanisms. Their main effects include preserving tight-junction integrity, redox and immune homoeostasis, microbial balance, epithelial hydration, and cellular metabolism. Importantly, improvements in nutrient utilisation are not consistently accompanied by increased nutrient transporter gene expression. Instead, the available evidence suggests that many nutritional interventions preserve absorptive capacity indirectly by maintaining the structural, metabolic and electrochemical conditions required for transporter function. This distinction is particularly relevant because transporter mRNA abundance alone does not necessarily reflect protein abundance, membrane localisation or actual transport capacity. Therefore, future studies should integrate transcriptional data with transporter protein expression, apical membrane localisation and functional measurements such as substrate flux or direct absorption assays. Such studies should also account for differences in heat-stress duration and severity, as well as bird type and production stage. Collectively, these findings support a functional rather than exclusively transcriptional approach to nutritional modulation of the gut barrier–nutrient transporter interface under heat stress.