Thermal comfort thresholds for Japanese quails based on performance and egg quality

Knowledge of the effects of thermal stress on Japanese quails helps support decision-making regarding the management of climate control systems. Thus, the objective of this study was to evaluate the performance and egg quality of Japanese quails subjected to different air temperatures (t_air) and to propose thresholds for the temperature-humidity index (THI), the Black globe humidity index (BGHI), and enthalpy (H). Two experiments (21 days each) were conducted in four climate-controlled wind tunnels. In the first experiment, t_air was 20, 22, 24, and 26 °C, and in the second, t_air was 20, 28, 30, and 32 °C. The relative humidity (RH) and air velocity were 60% and 0.3 ms^-1, respectively. To define the comfort thresholds, the productive performance of the birds, water intake, and egg quality were evaluated. No differences were observed (p > 0.05) for the performance-related variables, except for feed intake, which decreased (p < 0.05) as t_air increased, and water intake, which increased (p < 0.5) by 15.9% starting at 28 °C. For experiments 1 and 2, with t_air at 20 °C (t_air,obs = 20.8 and 21.3 °C, respectively), there was evidence of cold stress. The shell thickness, Haugh unit, and internal quality unit were negatively influenced (p < 0.05) by t_air starting at 28 °C. Japanese quails were able, within certain limits, to adapt to continuous thermal stress. The Japanese quails thermal comfort intervals recommended for THI, BGHI, and H are 68.4 to 76.2, 69.1 to 77.2, and 50.5 to 67.2 kJ kg_{dry air}^-1, respectively.