In order to better understand the metabolic changes leading to death which take place in the chicken during acute heat stress, the blood composition was determined in surviving and non-surviving chickens. The following blood analytes were determined: glucose, uric acid, serum total proteins, inorganic phosphate, total and ionized calcium, sodium, potassium, triiodothyronine, thyroxine. The haematocrit, erythrocyte creatine kinase (total and the isoenzymes) and haemoglobin fractions were also measured. Blood was taken from the wing vein before and after heat stress.Eight-week-old "Anak 2000" broilers were kept in a climate chamber at 24 °C/40% relative humidity during a 14-hour day, and at 20 °C/40% relative humidity during a 10-hour night. The birds were subjected to heat stress by exposing them to 40 °C/30% relative humidity for 3 hours.Significant differences between heat-stressed surviving and non-surviving chickens were seen in the blood levels of glucose, uric acid, total and ionized calcium, potassium, triiodothyronine, erythrocyte creatine kinase (total and isoenzymes). Differences were also seen in the levels and ratio of the 2 haemoglobin fractions.The significance of these changes, and their potential use as markers for heat resistance is discussed.

To cite this article: V. Pech-Waffenschmidt , E. Bogin , Y. Avidar & P. Horst (1995) SUMMARYRhode Island Red layers, consisting of four genetically different feathering typesfully 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°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 elecrolytes homeostasis.Reduced plumage seems to contribute to a greater resistance to hyperthermia caused by high ambient temperatures.