Intra-ruminal gas-sensing in real time: a proof-of-concept

An intra-rumen (IR) gas-sensing system incorporating commercially available gas sensors [methane (CH4), carbon dioxide (CO2) and hydrogen (H2)] and a wireless sensor network was developed to measure rumen gas concentrations of grazing animals in real-time. The IR gas-sensing devices also measure temperature and pressure near the sensors and the design isolates the electronics and battery from exposure to gases. Membranes were developed that allow the desired gases to diffuse through to the sensors while excluding corrosive hydrogen sulfide (H2S). Performance of the prototype IR devices was tested in cattle and sheep fed once a day as a proof-of-concept. Concentrations of expired gases from respiration chambers were compared with the concentrations obtained by the IR gas-sensing device within the rumen digesta. Direct measurements of rumen gas cap samples demonstrate a similar gas profile to that observed with the IR gas-sensing device with the ratio of CO2:CH4 peaking shortly after feeding and CO2 levels nearly 2.5 times greater than those of CH4. The gas ratio then declines over time to a point when at 23 h post-feeding the concentration of CH4 exceeds that of CO2. The H2 gas concentration in the rumen varied throughout the day reaching maximum levels of 2500 ppm after feeding and declining to 250 ppm over the day. Although the IR device was able to detect H2 in the rumen throughout the entire day, expired H2 was often below the limits of detection in the respiration chamber. Current work is focussed on extending the longevity of the devices in the rumen so that replicated trials can be performed on the accuracy and precision of the measurements.