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) concentrations have to be measured at certain intervals. The maximum and minimum values in the kinetics of CH emissions can be missed during the interval between measurements, which may influence the quantification of CH emissions. Chambers must be opened for morning feeding and cleaning, which causes a loss of CH data. Calculation methods are needed to estimate the lost CH emission data, which may influence the estimated amount of daily CH emissions. In this study, we measured the CH 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 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 emissions. The missing 1-h kinetics of CH emissions before feeding were not measured, and 2 calculation methods were used to estimate the missing 1-h kinetics of CH 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 emission from 10 heifers varied from 4.56 to 11.42 g/h. The increment of intervals decreased maximum rate of CH emission and increased minimum rate of CH emission. Interval caused less than 5% of the difference in measuring CH emissions. Although the mean method had greater estimated daily CH 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 emission measurements.