Bioenergetic Dynamics of Heat Exchange in Japanese Quail Under Heat Stress with Gracilaria birdiae Supplementation

The intensification of poultry production, associated with climate change, has increased the occurrence of heat stress, compromising animal welfare and productive efficiency. Despite recent advances, studies quantifying heat exchange in quail under different environmental and dietary conditions from an integrated bioenergetic perspective remain scarce, particularly regarding the shift between sensible and latent heat dissipation mechanisms. In this context, this study aimed to quantify and model sensible and latent heat exchange, together with associated physiological responses, in Japanese quail (Coturnix coturnix japonica) subjected to different air temperatures and dietary inclusion levels of the macroalga Gracilaria birdiae. A total of 864 quail were distributed in a completely randomized design, arranged in a 4 × 3 factorial design with four macroalgae inclusion levels (0.00, 3.00, 6.00, and 9.00%) and three air temperature levels (25.00, 29.00, and 33.00 °C), and maintained in climate-controlled chambers. Heat exchange was estimated using biophysical models integrating convective, radiative, and evaporative heat fluxes. Increasing air temperature reduced sensible heat exchange and intensified latent heat losses (p < 0.0001). During the growing phase, approximately 73.18% of sensible heat exchange was dissipated through radiation. In the laying phase, reductions of up to 59.96% in sensible heat exchange were observed, along with increases exceeding 50.00% in latent heat losses and reductions of up to 26.00% in total heat exchange. Increasing air temperature promoted higher respiratory rate (p < 0.0001), whereas surface and cloacal temperatures remained within the physiological range required to maintain homeothermy. Dietary inclusion of up to 9.00% G. birdiae exerted only limited effects on the quantified heat exchange pathways and did not impair physiological thermoregulation under the experimental conditions evaluated. No significant interaction between air temperature and dietary supplementation was observed for the heat exchange variables (p > 0.05). These findings show that heat stress was the primary determinant of bioenergetic heat exchange, whereas dietary supplementation with G. birdiae exerted only limited effects.