Circulating hormonal and gene expression profile in heat-stressed broilers divergently selected for high or low water efficiency

Warming climates and tightening water supplies are putting increasing strain on poultry production sustainability, especially in fast growing broilers that are highly susceptible to heat stress (HS). Boosting internal water use efficiency has therefore become a central goal for maintaining growth and performance under these conditions. However, the physiological mechanisms that support water-use efficiency, especially under chronic HS, remain poorly understood. In this study, we determined the effect of chronic HS on circulating hormone levels and gene expression in two broiler lines divergently selected for high (HWE) or low (LWE) water efficiency. From day 29 to 49, birds were raised under thermoneutral conditions (25°C) or exposed to daily HS- (36°C for 9 hours) in a 2 × 2 factorial design. On day 49, blood was collected for ELISA-based hormone analysis, and qPCR were used for gene expression. Data were analyzed by two-way ANOVA and Tukey multiple comparison test and significance was set at P < 0.05. The results illustrate that plasma corticosterone (CORT) and cortisol levels were significantly lower in HWE compared to their LWE counterparts, indicating a lower systemic stress status in HWE. Chronic HS significantly reduced the plasma levels of these stress hormones, suggesting potential physiological adaptation. At the molecular levels, chronic HS significantly down regulated the expression of adiponectin, glucagon, visfatin, orexin and its related receptors (ORXR1 and 2), arginine vasopressin system (AVT, V1aR, V1bR, V2R), and renin-angiotensin system (REN, AGT, AT1, AT2, and ACE). Together, these systemic changes suggest a shift and modulation in stress-, energy- and water-balance pathways toward adaptive, protective and homeostatic states.