Metabolic and biochemical changes during heat stress in relation to the feathering degree of the domestic hen.

Rhode Island Red layers, consisting of four genetically different feathering types- fully feathered (nanaff), fully frizzled feathered (nanaFf), naked neck (Nanaff), naked neck frizzled type (NanaFf)- were exposed to heat stress, and the physiological and metabolic responses were evaluated according to the feathering degree. Heat stress conditions (34 degrees C and relative humidity of 45%) were maintained for 8 weeks. Body temperature measured at different points, body characteristics and blood gas and electrolytes were determined and related to the environmental heat conditions. A plumage reduction led to higher body surface temperature, improved heat loss and, consequently, lower body-core temperatures. This was accompanied by a reduced polypnoea as reflected by higher blood levels of CO2, and smaller increases in blood pH and alkalosis with better stabilization of acid-base balance and electrolytes homeostasis. Reduced plumage seems to contribute to a greater resistance to hyperthermia caused by high ambient temperatures.