1985 Volume 56 Issue 12 Pages 925-930
The present study was undertaken to investigate the effects of high environmental temperature on the rectal temperature (RT), respiration rate (RR), heart rate (HR) and electrocardiogram (ECG) in constrained hens. Nine laying commercial White Leghorn hens at ages of 8 to 9 months were constrained by having their wings and legs tied and being enclosed in small experimental cage. They were placed in an artificial climatic chamber. The temperature in the chamber was gradually increased from 25 to 44°C at a rate of about 6min for 1°C. The relative humidity was controlled at above 90%. 1) RT, RR and HR did not respond to an environmental temperature below 28°C. 2) When the environmental temperature was raised from 29 to 34°C, RR increased with initiation of panting. However, changes in RT and HR were very slight. This suggests that the acceleration of RR might be effective for heat loss. 3) RT, RR and HR increased remarkably within a temperature range from 35 to 38°C. This suggests that heat loss due to panting might be insufficient to prevent increase in RT. 4) RR and HR decreased gradually at an environmental temperature above 39 to 41°C, respectively. Respiratory disorder was observed in depth and rhythm. In the ECG, atrioventricular conduction defects or ventricular premature contraction, such as paroxysmal ventricular tachycardia, ventricular fibrillation and flutter were observed. The hens fell into heat exhaustion 125 to 170min after exposure to high environmental temperature under constrained conditions.
