Effect of ambient temperature on dietary energy partitioning and utilization in broilers as measured by closed-circuit indirect calorimetry system

This study investigated the effects of ambient temperatures on growth performance and energy partitioning in broilers using a computer controlled closed-circuit indirect calorimetry system. Sixty 21-day-old male Arbor Acres broilers (1,004 ± 11 g BW) were randomly allocated to 4 ambient temperatures treatments (23°C, 25°C, 27°C, 29°C), with five indirect calorimetry chambers per treatments and three broilers per chamber. Broilers were fed the same test diet, and growth performance, gas exchange, dietary energy partitioning, and substrate oxidation were determined from d 25 to 28. Increasing ambient temperature from 23°C to 29°C resulted in linear increase ( P ≤ 0.036) in BW, metabolic BW, and ADG, whereas ADFI/ADG decrease linearly ( P = 0.019). Daily O 2 consumption and CO 2 production also decreased linearly with increasing ambient temperature ( P ≤ 0.003). Compared with broilers maintained at 23°C, those maintained at 29°C exhibited lower heat increment ( HI ) and HI/AME ( P ≤ 0.017), but greater net energy (NE) , retained energy ( RE ), NE/GE, NE/AME and RE/AME ( P ≤ 0.047). Regression models incorporating NE or RE intake, together with CP and MCP intake, produced higher R² for predicting ADG than the corresponding model based on AME, CP, and MCP intake. Ambient temperature had no significant effects on substrate oxidation or the contribution of carbohydrate, fat, and protein oxidation to total heat production. In conclusion, increasing ambient temperatures within the tested range improved dietary energy utilization efficiency, as reflected by higher NE and RE, lower HI, and a linear decrease in ADFI/ADG. The superior predictive performance of NE- and RE-based models further supports the use of NE and RE as more physiologically relevant indicators of dietary energy value than AME. These results demonstrate that closed-circuit indirect calorimetry is an effective approach for evaluating dietary energy partitioning under different thermal environments.