The influence of breath concentration in the gas sample on the accuracy of methane to carbon dioxide ratio using the sniffer method in dairy cows

Abstract

The purpose of this study was to investigate the carbon dioxide (CO₂ ) concentration in the sampled gas to avoid low concentration of breath while measuring the methane (CH₄ )/CO₂ ratio using the sniffer method. This study also assessed the effect of selective elimination by applying the threshold of CO₂ concentration to the CH₄ /CO₂ ratio. The gas measurement in the automatic milking system was conducted with 26 multiparous Holstein cows using an electric fan to manipulate the CO₂ concentration in the sampled gas. Four different thresholds of the background-corrected CO₂ concentrations (0, 0.025, 0.05, and 0.1%) were applied to every 1-s value of the individual gas measurement. Subsequently, three different upper limits of the proportion of eliminated values (none, 0.5, and 0.33) were applied to the individual records per milking. The results showed that the sampled gas must contain more than 0.1% of the corrected CO₂ concentration to enable accurate calculation of the CH₄ /CO₂ ratio. It is recommended that at least half of the values in the data be larger than the threshold of the corrected CO₂ concentration for unbiased measurement of the CH₄ /CO₂ ratio.

Keywords: automatic milking system; concentration of breath; methane to carbon dioxide ratio; sniffer method.