Mechanistic roles of chromium, zinc and selenium in heat-stressed poultry: endocrine, redox, gut and immune pathways

SUMMARYHeat stress (HS) remains a major constraint to poultry production, particularly in modern broiler, layer and duck genotypes characterised by high metabolic heat output and limited thermoregulatory capacity. Beyond reduced feed intake, HS induces a systems-level pathophysiology characterised by endocrine dysregulation, oxidative and proteotoxic stress, intestinal barrier failure, and immune suppression. Precision trace element nutrition has therefore gained attention as a mechanistically targeted strategy to enhance thermotolerance. This review synthesises current evidence on the mechanistic roles of chromium (Cr), zinc (Zn) and selenium (Se) in mitigating HS-induced dysfunctions in poultry. Chromium primarily stabilises endocrine–metabolic control by improving insulin sensitivity, reducing corticosterone output and supporting thyroid hormone activity, thereby indirectly limiting oxidative burden and excessive heat shock protein expression. Zinc and Se provide complementary cytoprotective actions by reinforcing antioxidant and redox-buffering systems, including Cu/Zn-SOD, metallothionein induction and Se-dependent selenoproteins such as glutathione peroxidases and thioredoxin reductases. At the intestinal level, these trace elements support epithelial integrity, redox balance and nutrient transport capacity, while collectively modulating inflammatory signalling pathways, dominated by NF-κB activation and Nrf2 suppression, during HS. Immune competence is preserved through coordinated reductions in oxidative injury, inflammatory cytokine production and endocrine-driven immunosuppression. In conclusion, the evidence indicates that Cr, Zn and Se act through distinct yet convergent endocrine, redox, gut and immune pathways, and that their combined use at physiologically appropriate levels provides greater protection than single-element strategies. Understanding these mechanistic interactions is essential for developing precision trace element programmes to sustain poultry health, welfare and productivity under increasing thermal stress.