Comparative Analysis of Enteric Methane Emissions in Lactating Holstein Cows Using the GreenFeed Monitoring System and the Sniffer Method

This study aimed to evaluate two different spot-sampling methods—the sniffer-based method (SB) and the GreenFeed system (GF)—for estimating enteric methane (CH<sub>4</sub>) emissions in dairy cows. Specifically, this study was performed to determine whether the SB using a gas hood system could serve as an acceptable alternative to the GF under practical on-farm conditions. A total of 24 lactating Holstein cows were used across three experimental phases (n = 24). CH<sub>4</sub> emissions were measured eight times over four consecutive days in each phase, with measurements taken twice per phase using both the GF and SB. CH<sub>4</sub> emissions from the SB were estimated by applying the CH<sub>4</sub>-to-carbon dioxide ratio to a previously validated prediction equation. Results showed that the GF tended to report higher CH<sub>4</sub> emissions (312.9 ± 56.50 g/d) compared to the SB (297.1 ± 61.83 g/d). Bland–Altman analysis showed acceptable agreement between methods, with a bias of 15.78 g/d and 95% limits of agreement ranging from –96.12 to 127.68 g/d, corresponding to 7.1% of the total range. For the CH<sub>4</sub>-to-carbon dioxide ratio, the SB produced consistently higher values (0.077 ± 0.012) than the GF (0.064 ± 0.011). Bland–Altman analysis for the CH<sub>4</sub>-to-carbon dioxide ratio indicated a small mean bias (–0.012) and minimal proportional deviation (21.3%). Variance homogeneity testing using the Brown-Forsythe test indicated no significant method-dependent differences in CH<sub>4</sub> emission variability across experimental phases (<italic>p</italic> = 0.104). Phase-specific performance of the SB showed acceptable agreement with the GF, with mean absolute percentage errors ranging from 11.57% to 19.20% and confidence rates between 80.80% and 88.43% across phases. In summary, the SB provided CH<sub>4</sub> estimates comparable to those from the GF across all experimental phases. Given its advantages such as portability, flexible installation, and low operational cost, the SB represents a feasible and accessible alternative for on-farm quantification of CH<sub>4 </sub>emissions in dairy cows. Together, these findings indicate that the SB provides acceptable estimates of CH<sub>4</sub> emissions from lactating Holstein cows under on-farm conditions, making it a feasible on-farm measurement method alternative to the GF.