Association Between Methane Concentration Measured by a Modified Mask System and GreenFeed Methane Production in Dairy Cows.

Accurate measurement of enteric methane (CH4) emissions is essential for methane phenotyping, but established techniques may be costly and difficult to apply to large numbers of animals. This study evaluated a simple mask-based system for measuring CH4 concentration in exhaled breath of lactating dairy cows in comparison with CH4 production measured using GreenFeed. Thirty-two Holstein cows were evaluated, generating 60 paired observations. On each sampling day, exhaled breath was collected using the mask during three 5 min periods, and CH4 concentration was determined by micro gas chromatography. Mask CH4 concentration was positively associated with GreenFeed CH4 production (Pearson r = 0.616; Spearman ρ = 0.606; p < 0.001). The association remained significant after accounting for repeated observations within cows using a linear mixed-effects model (β = 53.1 ± 15.7 g/day per 0.1 percentage-point increase in mask CH4, 95% CI: 22.3 to 84.0; p < 0.001). An exploratory within-cow analysis was also performed in four cows evaluated over five sampling days. Positive within-cow correlations were observed in all four animals (r = 0.157-0.699), but none reached statistical significance (p > 0.05). These results indicate that CH4 concentration measured using the mask contains information on differences in methane emission among cows and may have potential as a methane phenotyping measure.