Technical note: Evaluation of interval between measurements and calculation method for the quantification of enteric...

Respiration chambers share one analyzer working in parallel, and methane (CH₄) concentrations have to be measured at certain intervals. The maximum and minimum values in the kinetics of CH₄ emissions can be missed during the interval between measurements, which may influence the quantification of CH₄ emissions. Chambers must be opened for morning feeding and cleaning, which causes a loss of CH₄ data. Calculation methods are needed to estimate the lost CH₄ emission data, which may influence the estimated amount of daily CH₄ emissions. In this study, we measured the CH₄ 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 CH₄ 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 CH₄ emissions. The missing 1-h kinetics of CH₄ emissions before feeding were not measured, and 2 calculation methods were used to estimate the missing 1-h kinetics of CH₄ 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 CH₄ emission from 10 heifers varied from 4.56 to 11.42 g/h. The increment of intervals decreased maximum rate of CH₄ emission and increased minimum rate of CH₄ emission. Interval caused less than 5% of the difference in measuring CH₄ emissions. Although the mean method had greater estimated daily CH₄ emission than the nearest method, the difference was within 3%. The interval between measurements (≤3 h) and calculation method had little influence on enteric CH₄ emission measurements.