SCOUT: Closed-Loop In Vivo System for Continuous Methane Concentration Monitoring in Cattle

Enteric methane measurement from ruminant livestock faces fundamental trade-offs between accuracy and operational feasibility. Existing methods quantify methane after eructation and atmospheric dilution, limiting temporal resolution and confounding biological signals with environmental variables. We present the Smart Cannula-mounted Optical Unit for Trace methane (SCOUT), an autonomous system for continuous in vivo monitoring of ruminal headspace methane concentrations. SCOUT uses a closed-loop gas recirculation circuit that samples the headspace continuously without venting gas to the atmosphere and mounts onto a standard cannula plug without degrading its seal integrity. SCOUT was deployed on cannulated Simmental heifers under contrasting dietary treatments. Headspace concentrations were two to three orders of magnitude above concurrent ambient sniffer readings, providing substantially greater signal resolution for characterizing methane dynamics. High-frequency monitoring revealed concentration changes associated with postural transitions and feeding on timescales inaccessible to ambient methods. Cross-platform comparison with ambient sniffers showed that eructation events produced the expected inverse concentration signature, supporting the validity of the in vivo concentration signal. These results demonstrate that the rumen headspace contains continuous, biologically interpretable methane signals that SCOUT can reliably access, establishing the measurement infrastructure necessary for developing concentration-to-flux models that would support precision phenotyping, emission proxy calibration, and mitigation strategy evaluation.