Comparative analysis of respiratory metabolism, blood physiology, antioxidant capacity, and hypoxia-related gene expression in Snowy White chickens raised at high and low altitudes.

Understanding the physiological and molecular mechanisms underlying altitude adaptation is critical for optimizing poultry health and performance in diverse environments. This study comparatively evaluated the respiratory metabolism, hematological profiles, antioxidant capacity, immune status, and hypoxia-related gene expression in Snowy White chickens raised at contrasting altitudes. A total of 380 chickens from a low-altitude region (Sichuan) and 550 from a high-altitude region (Tibet) were reared under standardized dietary and management conditions. The results should that key indicators of anaerobic metabolism, including serum lactate and lactate dehydrogenase (LDH) levels, were significantly elevated in high-altitude chickens, indicating greater reliance on glycolysis under hypoxic stress (P < 0.05). Hematological analysis revealed significantly increased red blood cell (RBC) count, hemoglobin concentration, hematocrit, and mean corpuscular hemoglobin in high-altitude birds (P < 0.05), while mean corpuscular volume (MCV) was higher in low-altitude chickens (P < 0.05), reflecting divergent strategies in oxygen transport efficiency. Oxidative stress markers showed that high-altitude chickens had elevated malondialdehyde (MDA) levels, indicating increased lipid peroxidation, whereas low-altitude chickens demonstrated superior antioxidant defense, with significantly higher total antioxidant capacity (T-AOC) and total superoxide dismutase (T-SOD) activity (P < 0.05). In addition, immunoglobulin levels (IgM and IgG) were markedly higher in low-altitude chickens, suggesting enhanced immune responsiveness. Furthermore, qRT-PCR revealed elevated expression of hypoxia-related genes including hypoxia-inducible factor 1-alpha (HIF-1A), endothelial PAS domain-containing protein 1 (EPAS1), vascular endothelial growth factor (VEGF), and erythropoietin (EPO) in the heart, lungs, and kidneys of the high-altitude chickens (P < 0.05), while egl-9 family hypoxia-inducible factor 1 (EGLN1) expression was significantly downregulated in these tissues. These physiological and molecular adaptations highlight the mechanisms by which Snowy White chickens maintain homeostasis under chronic hypoxic stress and offer insight into genetic and metabolic pathways supporting high-altitude resilience. Taken together, these findings offer valuable insights into high-altitude resilience in avian species and may inform breeding strategies for improved adaptability to hypoxic environments.