The objective of this study was to develop a facemask system and evaluate its potential for measuring enteric CH4 and CO2 production. Recovery tests were conducted and resulted in 99.0% (SD, 3.2) and 102.3% (SD, 2.6), respectively. An experiment was conducted and the facemask system was compared with the GF system. Five mid-lactation cows were fed a lactation diet ad libitum (Period 1) for 5 days and then fed the same diet at 90% of the ad libitum intake for 5 days (Period 2) where CH4 and CO2 productions were measured at the end of each period. While daily CH4 and CO2 productions were different (p ≤ 0.04) between Period 1 and 2, those did not differ between the methods, and no interaction between period and method was observed. A linear regression analysis indicated a good correlation for CH4 (CCC = 0.72; RMSE = 22% of the mean) and CO2 (CCC = 0.79; RMSE = 10% of the mean) between the facemask and the GF system, while systemic bias was observed for CO2. In conclusion, the facemask system developed has the potential to measure CH4 and CO2 production from lactating cows and the measurement was similar with that from the GF system.
Bae et al. (2026) studied this question.