Technical note: Evaluation of interval between measurements and calculation method for the quantification of enteric methane emissions measured by respiration chamber.

Respiration chambers share one analyzer working in parallel, and methane (CH ₄ ) concentrations have to be measured at certain intervals. The maximum and minimum values in the kinetics of CH ₄ emissions can be missed during the interval between measurements, which may influence the quantification of CH ₄ emissions. Chambers must be opened for morning feeding and cleaning, which causes a loss of CH ₄ data. Calculation methods are needed to estimate the lost CH ₄ emission data, which may influence the estimated amount of daily CH ₄ emissions. In this study, we measured the CH ₄ emissions of 10 growing Chinese Holstein dairy heifers in respiration chambers. Methane concentrations were measured every 0.5 min to obtain the 23-h kinetics of CH ₄ emissions, which were further selected at different intervals between measurements (i.e., 5, 30, 60, 120, 180, and 240 min) to evaluate the effects of interval on quantification of CH ₄ emissions. The missing 1-h kinetics of CH ₄ emissions before feeding were not measured, and 2 calculation methods were used to estimate the missing 1-h kinetics of CH ₄ emissions: mean value of measuring period (the mean method) and the nearest value of measurement just before chamber opening (the nearest method). The results showed that the rates of CH ₄ emission from 10 heifers varied from 4.56 to 11.42 g/h. The increment of intervals decreased maximum rate of CH ₄ emission and increased minimum rate of CH ₄ emission. Interval caused less than 5% of the difference in measuring CH ₄ emissions. Although the mean method had greater estimated daily CH ₄ emission than the nearest method, the difference was within 3%. The interval between measurements (≤3 h) and calculation method had little influence on enteric CH ₄ emission measurements.
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