The physiological and biochemical responses of broilers exposed to short-term thermal stress

Abstract

1. 1. Exposure of cockerels to heat stress (42°C) for 15 min resulted in a reduction of both the total free and essential free amino acids in plasma with simultaneous elevation in the levels of the total free and essential free amino acids in liver as compared to the pre-stress level. 2. 2. The reduction in the plasma free amino acid pools was accompanied by a decrease in total proteins and alkaline phosphatase concentrations, with a simultaneous elevation in albumin, glucose, uric acid, plasma free fatty acids, lactate dehydrogenase and creatine kindase. 3. 3. During the recovery period both the total plasma and hepatic free amino acids returned to prestress levels but the levels of the essential plasma free amino acids in heat-stressed birds remained low while the hepatic essential free amino acids remained high. 4. 4. At the end of a 30 min recovery period at 21°C, the glucose content substantially decreased with free fatty acids and uric acid still remaining at high levels. 5. 5. There was a significant reduction in nitrogen retention in heat-stressed birds determined during the 24 hr recovery period mainly due to an increase in the excretion of nitrogen in uric acid form. 6. 6. In birds exposed to cold (4°C), the only significant changes were an increase in the hepatic essential free amino acids and an increase in uric acid excretion. 7. 7. The results indicate that short-term heat stress affects protein metabolism in growing chickens.