Measurement methods to assess methane production of individual dairy cows in a barn

Mitigation of methane production from dairy cows is critical to reduce the dairy industry’s contribution to the production of greenhouse gases. None of current used methane measurement methods are flawless and application of the methods is limited to assess the effects of methane mitigation methods under practical conditions. The main objective of this thesis is to design, test, and validate methods to determine or rank the methane production of individual dairy cows at farm house level.

As a start, I evaluated merits and drawbacks of existing methane measurement methods and discussed against 14 requirements of methane measurement methods to assess methane mitigation strategies. This review study revealed that none of existing methods meet all requirements, and pointed out that sampling of breath air during the lying period of cows in cubicles could be a practical direction to measure methane production of individual cows under farm conditions. Therefore, we first assessed methane concentration levels and variations in time, and around cubicles, explored effects of barn and management factors on them, and assessed the effect of the variation of the background methane concentrations on assessing methane production of individual dairy cows in cubicles. Then, we designed and constructed an artificial reference cow (ARC) that mimics the methane production of real cows with known pre-set methane production rates and dynamics of eructations. With the acquired background information and the developed ARC, we assessed the uncertainty of a breath methane concentration (BMC) method in a feeder and developed a cubicle hood sampler (CHS) that measures methane fluxes from lying cows in cubicles. The observed uncertainty related to random errors of the BMC method can be overcome by sufficient numbers of repetitions. However identified uncertainty with a systematic nature, related to inconsistent relation between concentration and production rate, cannot be compensated by repeated measurements and requires further investigation into the widely used BMC method before it can be used with confidence. Compared to the BMC method, the developed CHS is not subject to such systematic effects and allows prolonged measurement periods. Performance test under field conditions showed that the designed CHS accurately measured methane fluxes provided by the ARC.

Overall, in this thesis I assessed the measurement error of current three methane measurement principles (flux, breath concentration & tracer gas), provided information to limit the measurement variation, and assessed the availability to determine or rank the methane production of individual dairy cows at farm house level. The newly developed ARC can be used as a known reference source to calibrate and develop practical methane measurement methods, and the CHS is sufficiently accurate to measure methane production of individual cows at farm house level.