Measuring the Respiratory Gas Exchange of Grazing Cattle Using the Greenfeed Emissions Monitoring System

Ruminants are a source of enteric methane, which has been identified as a greenhouse gas that contributes to climate change. With interest in technologies to decrease enteric methane emission, novel systems are currently being developed to measure the methane emission by cattle. An issue with grazing cattle is the ability to measure emissions in open-air environments. A scientific instrument for this task is the GreenFeed emission monitoring system (GEM; C-Lock, Inc.; Rapid City, SD). The GEM is a head-chamber that grazing cattle occasionally visit and while the animal consumes a small portion of bait (3 to 8 min), the GEM captures the animal’s breath cloud by exhausting air through the system. The breath cloud is then analyzed for methane and carbon dioxide. Data are hourly uploaded to a server where it is processed using algorithms to determine total daily emissions. Several factors affect the emission estimates generated by the GEM including the animal’s visitation rate, length of sampling period, and airflow through the GEM. The location of the GEM is an important factor in determining the cattle’s willingness to visit it. Further, cattle need to be trained to use the GEM, which normally requires 4 to 8 wk. Several researchers have shown that 30 or more visits are required to obtained high-quality estimates of emissions. Once cattle are trained to use the GEM, the bait delivery rate has little effect, as long as visitation length is greater than 3 min. Airflow through the GEM is an important factor, but as long as airflow is maintained above 26 L/s breath-cloud capture seems complete. There is great concern regarding diurnal variation in the instantaneous production rates of methane because the GEM only spot-samples 3 to 4 times/d. Preliminary analysis have shown that the variation in the instantaneous production rates of methane do not vary as greatly with grazing cattle compared to meal-fed cattle; hence, the variation can be managed. It seems that increasing the visitation length decreases variation in emission estimated, but there is a diminishing return to increasing visitation length. Post-processing of emissions data is a critical part of the quantification process. Post-processing data from situations where correction is needed has been shown to be successful and to improve the quality of estimates. The GEM is a useful tool for researching the nutrition and emissions of grazing cattle, but great care must be taken to obtain the best quality data possible.