Development of a mobile, open-circuit indirect calorimetry system

Abstract

A system for the rapid determination of O2 consumption, CO2 production and subsequent indirect estimation of energy metabolism of ruminants has been updated and validated. The accurate determination of gas temperature, relative humidity, absolute pressure and flow is important to the overall use of the system. Analogue outputs from the specific analyzers were multiplexed and then routed to a data acquisition system with appropriate software control. Subsequent data processing included modification to fit LOTUS 1-2-3 files. The analyzers were calibrated with standard test gases for the gas meters. In an experimental confirmation trial, eight sheep were fed at maintenance (M) or 2× maintenance (2M) or fasted 48 h after each level of intake (MF and 2MF, respectively) and subsequent energy metabolism was determined. Oxygen consumption (mL min−1), metabolic rate (W) and CO2 production (mL min−1) were greater (P < 0.05) for animals fed 2M (111.2, 379.5 and 101.9, respectively) than for those fed M (85.4, 291.2 and 86.1, respectively). Maintenance values were, in turn, also higher (P < 0.05) than those for either MF (56.7, 193.4 and 48.0, respectively) or 2MF (54.6, 186.4 and 46.3, respectively). M sheep had a higher respiratory quotient (1.03) (P < 0.05) than either MF sheep (0.86) or 2MF sheep (0.89), with 2M sheep being intermediate (0.95). There were no differences (P > 0.05) between the two fasted states for all parameters. Results from the confirmation experiment agree with previously published work and were consistent with those from similar systems. Key words: Indirect calorimetry, oxygen consumption, sheep