Validation of the methane production measurement accuracy and ranking capacity of portable accumulation chambers for use with small ruminants

Abstract

Using portable accumulation chambers (PAC) is an attractive approach to recording methane (CH4) production of small ruminants. Mass flow controllers (MFC), for their part, are an effective way of validating PAC measurements, as they allow to simulate methane production rates freely of extraneous factors. The present study describes a series of tests carried out to evaluate the accuracy and precision of methane mass recordings of eight PAC against known CH4 masses released by a MFC. Across the tested range, the PAC were able to recover between 67.6 and 74.5% of the true CH4 released. No significant differences were detected between the different PAC, but a statistically significant linear shift was detected over the mass range. Therefore, PAC as currently used are not well suited for applications looking at absolute production levels requiring high absolute accuracy. If recovery tests are conducted regularly across the measurement range, a calibration factor could be generated to correct for the inaccuracy. These PAC were however well suited for investigating relative differences between animals, e.g. ranking animals to compare differences in CH4 production between breeds. The methane recordings made by these chambers were highly precise, with low coefficients of variation between replicates (0.0–2.4%) and high repeatability (>0.99). Furthermore, the correlation between released and recorded CH4 masses was very strong and positive (R > 0.99). Overall, the mass recovery test presented here provides a feasible method for harmonizing methane monitoring procedures using PAC between research groups, thereby improving joint efforts aimed at mitigating greenhouse gas production in small ruminants.