Thermoneutral zone of chickens as determined by measuring heat production, respiration rate, and electromyographic and electroencephalographic activity in light and dark environments and changing ambient temperatures

Abstract

Summary Electromyographic (EMG) activity, electroencephalographic (EEG) activity, heat production ( H ), respiration rate ( RR ), and body temperature ( T B ) of unacclimatized chickens were measured during periods of light and darkness at ambient temperatures ( T a ) between 7·7 and 37·7 °C. The difference between pectoral muscle and abdomen temperature was less than 0·1 °C over the entire temperature range. Body temperature increased (P ≤ O·l) when T a was above 27·5 °C and was higher in the light than in the dark (P ≤ 0·05). Respiration rate decreased significantly with increasing T a . The decrease, however, was not as great during the dark (P ≤ 0·05) as during the light period (P s£ 001). Heat production decreased (P ≤ 0·01) with increasing T a up to T a = 22·3 °C. There was no significant difference between heat production during the light period and that during the dark period. EMG amplitude declined (P ≤ 0·01) with increasing T a up to 27·5 °C in the light and 22·3 °C in the dark and was higher (P ≤ 0·05) in the light than in the dark. Mean frequency of EMG activity was independent of light and T a . The percentage of low-frequency EEG activity in the dark did not change significantly over the entire T a range, but in the light it decreased as T a increased above 25·7 °C (P ≤ 0·05). The percentage of high-frequency EEG activity appeared as a mirror image of low-frequency activity. Overall results indicated a thermoneutral zone between 32·2 and 37·7 °C in the light and between 27·5 and 37·7 °C in the dark.