Abstract
Eight commercial Single Comb White Leghorn hens were used to study the effects of high ambient temperature on behavioral activities and to select a better parameter for the estimation of heat production between activity count and standing time. The hens were kept at ambient temperatures of 25, 29, and 33°C and fed ad libitum. Daily feed intake and heat production decreased with the increase of temperature. Daily total standing time increased significantly with the increase of temperature, specially the increase occurred in the dark periods at 29 and 33°C, and were 247% (P<0.01) and 413% (P<0.01), respectively, compared to the standing time at 25°C. Heat production per hour decreased significantly (P<0.01) in both the light and dark periods with the increase of temperature. On the other hand, the daily activity counts were almost the same at all the temperatures. The levels of activity counts per hour increased significantly (P<0.01) during the dark periods at 29 and 33°C in comparison with that of at 25°C. Heat production per activity count decreased significantly (P<0.01) with the increase of temperature. The hens changed their behavioral pattern, and minimized heat production when introduced to higher temperatures. From the analysis of variance of the multiple regression equations, the contribution rates of activity counts (counts/h) and standing time (min/h) towards total heat production (kJ/kg0.75/h) were 65% and 23%, respectively. Therefore, activity counts give better results in regards to estimating heat production in White Leghorn hens.
