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

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.