All homeothermal animals including birds maintain a constant internal body temperature. According to thermodynamic basics, animals regularly exchange heat with the surrounding environment, but this mechanism is exactly efficient at the animal's thermoneutral range of environmental temperatures (Hannas,1999; El-Tarabany and El-Bayoumi,2015). When environmental temperatures exceed the thermoneutral range,rectal temperature elevates,as well as respiratory rate,where panting is a mechanism used by birds to promote evaporative heat loss,thereby attempting to preserve body temperature (Silvaetal.,2001).Thus environmental temperature and humidity are substantial factors affecting egg production. Birds raised at environmental temperatures outside their thermoneutral zone may suffer severe physiological changes,including decreased feed intake,decreased feed
efficiency and consequent drop in egg production and deteriorated egg quality,including light eggs,decreased yolk weight and percentage,and low specific gravity (Macari etal.,2004). To minimize these detrimental effects of thermal stress,many practical approaches have been suggested to enhance thermotolerance of birds, leading to minimize the adverse impacts on productivity (Del Vescoetal.,2014). Taking these facts into consideration,the aims of this tria lwere to elucidate the impact of temperature humidity index (THI )on egg quality traits in Japanese quail and estimate the correlations between external and internal egg quality traits.