Development of a computer-controlled closed-circuit respiratory calorimetry system to determine dietary energy utilization in broilers

Net energy (NE) is most precise measure of dietary energy for broilers, but its accurate determination requires a reliable respiratory calorimeter. This study developed a computer-controlled closed-circuit respiratory calorimeter to measure oxygen (O2) consumption, carbon dioxide (CO2) production, and energy utilization in broilers, and evaluated its accuracy and repeatability. Three groups of six closed-circuit calorimeters were randomly assigned to burn 100, 150, or 200 g of ethanol (purity ≥ 99.7%) to assess the accuracy of O2 usage and CO2 production. Subsequently, three groups of six calorimeters, each containing three male Arbor Acres broilers (body weight [BW] = 948 ± 14 g) as one experimental unit were used to test the repeatability of the chamber environment control, growth performance, and the determination of dietary energy utilization in broilers. Sensors automatically logged temperature, humidity, O2 and CO2 concentrations, O2 consumption, BW, and average daily gain (ADG). Data analysis was conducted using SAS 9.4 using the MEANS, GLM, and REG procedures. The relative ratios of actual O2 consumption and CO2 production to theoretical values (from complete ethanol combustion) ranged from 100.4% to 101.3% (P = 0.326), and 102.7% to 102.8% (P = 0.981), respectively, with all CV below 1.53%, demonstrating the system's accuracy and precision in quantifying respiratory gas exchange. The CV of inter-group (CVinter-group) for temperature, humidity, and O2 concentration were 0.08% (P = 0.664), 1.14% (P = 0.726), and 0.09% (P = 0.203), respectively. The CVinter-group for ADG, average daily feed intake (ADFI), and feed conversion ratio were 3.09% (P = 0.551), 2.24% (P = 0.580), and 2.11% (P = 0.364), respectively. The CVinter-group for O2 consumption and CO2 production were 1.21% (P = 0.903) and 1.86% (P = 0.758), respectively, and both factors were linearly related to BW0.70 and ADFI (R2 ≥ 0.889, P < 0.010). The CVinter-group for apparent metabolizable energy, total heat production, heat increment, NE, retained energy, NE deposited as protein or as fat ranged from 0.21% to 3.19% (0.236 ≤ P ≤ 0.903). These results demonstrate the system's high repeatability and precision in maintaining environment conditions and monitoring growth performance and energy partitioning in broilers. Thus, this system is a valuable tool for accurately evaluating energy utilization in broilers.