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 (CH4) 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). CH4 emissions were measured eight times over four consecutive days in each phase, with measurements taken twice per phase using both the GF and SB. CH4 emissions from the SB were estimated by applying the CH4-to-carbon dioxide ratio to a previously validated prediction equation. Results showed that the GF tended to report higher CH4 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 CH4-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 CH4-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 CH4 emission variability across experimental phases (p = 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 CH4 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 CH4 emissions in dairy cows. Together, these findings indicate that the SB provides acceptable estimates of CH4 emissions from lactating Holstein cows under on-farm conditions, making it a feasible on-farm measurement method alternative to the GF.