Potential applications of a low-cost gas sensor to monitor enteric methane emission from ruminant animals

Enteric methane (CH 4 ) emissions are a significant concern in ruminant production due to its high global warming potential of 28 times that of CO 2 . Research is focused on mitigating these emissions through animal and feed management. However, accurately and economically measuring CH 4 emissions from individual animals remains challenging due to current methods' high cost, slow speed, and labor intensity. Therefore, the primary objective of the present study was to evaluate low-cost gas sensors, named MQ-4, MQ-8, MQ-7, by comparing their data with a well-established GreenFeed system (GF). The MQ-4, MQ-8, and MQ-7are sensitive to CH 4 , H 2 , and CO, respectively. Sensors were assembled on a single board and placed at various points on the GF system (airflow outlet, pump outlet, and feed tray) to determine optimal placement. The pump outlet showed the highest correlation (r = 0.51 for CH 4 and r = 0.65 for H 2 ) with GF data. Following this, the gas sensors were placed in a pump outlet for 45 days, and enteric CH 4 and H 2 were measured simultaneously using both devices on 28 heifers, resulting in a total of 3.88 × 10 6 paired measurements. Correlation between CH 4 and H 2 data from the GF and gas sensors was assessed using Spearman correlation coefficients (SCC), repeatability, and peak measurement algorithms. The SCC values for the CH 4 concentration from the MQ-4 gas sensor and GF averaged weekly, daily, hourly, and minute were 0.62, 0.56, 0.49, and 0.47, respectively. The repeated measures correlation between (from the per second record) the devices was relatively low (0.30). The repeatability of CH 4 concentration was greater for the GF (0.31) than for the MQ-4 gas sensor (0.13). Additionally, there were significant differences in the detected number of peaks, peak duration, and width between the two devices. The peak detection algorithm indicated that the GF detected more peaks and processed data four times faster than the MQ-4 gas sensor. Although results indicate moderate and significant correlations between H 2 and CH 4 voltages measured by the GF and gas sensors, lower repeatability and discrepancies in peak characteristics observed for the gas sensor suggest caution in interchangeable use without further methodological refinement.