Modified approach to estimating daily methane emissions of dairy cows by measuring filtered eructations during milking

The aim of this study was to compare metrics for quantifying enteric methane (CH₄) emissions from individual cows during milking using frequent spot measurements and peak analysis methods. An infrared gas analyser was used to measure the CH₄ emitted by cows, and eructation peaks were identified using a Signal Processing Toolbox provided by Matlab. CH₄ emissions were quantified by gas peak height, peak amplitude and average concentration, and were expressed in grams per day and CH₄ yield (grams per kilogram of dry matter intake (DMI)). Peak analysis measurements of CH₄ were obtained from 36 cows during 2,474 milkings, during which cows were fed a ration containing between 39 and 70 % forage. Spot measurements of CH₄ were compared to a separate dataset of 196 chamber CH₄ records from another group of 105 cows, which were fed a ration containing between 25 and 80 % forage. The results showed that the metrics of CH₄ peak height and CH₄ peak amplitude demonstrated similar positive relationships between daily CH₄ emissions and DMI (both r = 0.37), and a negative relationship between CH₄ yield and DMI (r = -0.43 and -0.38 respectively) as observed in the chamber measurements (r = 0.57 for daily emissions and r = -0.40 for CH₄ yield). The CH₄ metrics of peak height and peak amplitude were highly repeatable (ranging from 0.76 to 0.81), comparable to the high repeatability of production traits (ranging from 0.63 to 0.99) and were more repeatable than chamber CH₄ measurements (0.31 for daily emissions and 0.03 for CH₄ yield). This study recommends quantifying CH₄ emissions from the maximum amplitude of an eructation.