Comparative evaluation of bags used to collect samples of oxygen, carbon dioxide, and methane for use in open-circuit indirect calorimetry

Methane (CH₄), carbon dioxide (CO₂), and oxygen (O₂) are the major gases produced by dairy cattle as a result of rumen fermentation and metabolism, and thus, their concentrations are frequently measured as a way of estimating heat production and energy metabolism. A well-utilized method of measuring gas consumption and production to estimate heat production is indirect calorimetry, which requires bags to retain the sampled gases until analysis. The objective of this study was to determine the ability of a polyvinyl fluoride gas bag (PF) and a multilayer fabrication gas bag containing an aluminum layer (NAP) to maintain respiratory gas composition in comparison to a polyethylene terephthalate bag (PET). For experiments 1 and 2, respiratory gases were collected from 6 multiparous, lactating Jersey cows using headbox-style indirect calorimeters. During experiment 1, PF and PET were used to sample respired gases of the headboxes for each cow. Experiment 2 used a similar design to compare NAP and PET. In both experiments, respired air was sampled into the gas bags for 5 h before being analyzed immediately to determine the concentrations of the gases. All bags were reanalyzed for gas concentrations at 24 and 72 h after sampling to determine the ability to maintain the concentration of gas over a 3-d period. In experiment 1, a tendency was observed for time by bag material interaction, as PET retained a consistent concentration of O₂ (20.37% ± 0.020%) over the 72-h period, whereas the O₂ concentration in PF increased from 20.37% to 20.47% ± 0.02%. Similarly for CO₂, PET maintained a consistent concentration of 0.653% ± 0.020% from hour 0 to 72, whereas PF significantly decreased from 0.65% to 0.55% ± 0.02%. No interactions between bag material and time occurred for CH₄ across 72 h for PET and PF, averaging 0.0421% ± 0.005%, respectively. In experiment 2, comparing NAP and PET, no bag material, time, or bag material by time interactions were observed for O₂ concentration, CO₂ concentration, or CH₄ concentration, averaging 20.37% ± 0.020% O₂, 0.648% ± 0.025% CO₂, and 0.0377% ± 0.0100% CH₄ between treatments. Results indicate a significant difference in gas concentrations over time for PF relative to PET, and no difference was observed in gas concentrations for NAP in comparison to the PET bag. Thus, gas bag material type and time to gas analysis should be considered to effectively characterize respiratory gas composition.