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 feat hering types-fully feathered (nanaff), fully frizzled feathered (nanaF f), naked neck (Nanaff), naked neck frizzled type (NanaFf)- were expos ed 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 envi ronmental heat conditions. A plumage reduction led to higher body surf ace temperature, improved heat loss and, consequently, lower body-core temperatures. This was accompanied by a reduced polypnoea as reflecte d by higher blood levels of CO2, and smaller increases in blood pH and alkalosis with better stabilization of acid-base balance and elecroly tes homeostasis. Reduced plumage seems to contribute to a greater resi stance to hyperthermia caused by high ambient temperatures.