Assessment of breath methane measurement with an artificial reference cow in the lab

To mitigate methane emission from dairy cows, the primary issue is to evaluate the efficacy of measures to reduce methane emission. To evaluate e.g. genetic differences and feeding measures in practice, we need a technique to assess the individual methane emission from a large number of cows in the barn. First, we designed and constructed an artificial reference cow that simulated exhalation and eructations of cows, with known methane production rates and representative release patterns. The methane mass balance of the artificial cow was extensively tested and results showed strong linear relation between controlled and measured methane mass. Methane concentration release patterns with a sinusoidal curve produced by five simulated cows were compared to patterns measured from real cows. Results showed small differences between simulated and real concentrations with respect to time interval of eructations and lowest and peak concentrations. We concluded that the artificial reference cow can be used as a known reference source to develop methane measurement methods. Second, the artificial cow was used in a typical setup for measuring methane concentrations in a feed bin, where a cow eats concentrates during milking in an automatic milking system. Methane concentration was continuously analysed in the sampled breath air. The objective of this study was to validate whether variation of methane production rates (set at five levels between 200 and 400 g/d, each level repeated 5 times) between cows and within time can be assessed. This was done under stable and turbulent aerial conditions. Results under stable conditions showed that imposed daily methane production had a strong linear relation with measured average methane concentration in the feeder. But preliminary results under turbulent conditions showed that the relation was more variable, probably due to the aerial turbulence in the barn.