Enteric methane emissions of beef cows grazing tallgrass prairie pasture on the southern Great Plains

Authors: Todd, Richard; Moffet, Corey; Neel, James; Turner, Kenneth; STEINER, JEAN - Retired ARS Employee; COLE, NOLE - Retired ARS Employee

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2019
Publication Date: 9/15/2019
Citation: Todd, R.W., Moffet, C., Neel, J.P., Turner, K.E., Steiner, J., Cole, N.A. 2019. Enteric methane emissions of beef cows grazing tallgrass prairie pasture on the southern Great Plains. Transactions of the ASABE. 62(6):1455-1465. https://doi.org/10.13031/trans.13341.
DOI: https://doi.org/10.13031/trans.13341

Interpretive Summary: Methane is a greenhouse gas that contributes to global warming and climate change. Cattle produce methane as a natural byproduct of digestion but measuring the methane that grazing cattle emit is challenging. A team of USDA-ARS scientists in Bushland, Texas, Woodward, Oklahoma and El Reno, Oklahoma studied methane emitted by grazing beef cows during one to two week-long campaigns during three seasons of the annual grazing cycle – summer, autumn and winter. We used three different methods to measure methane. On average, every day, each cow produced 0.74, 0.59 and 0.64 pounds of methane during summer, autumn and winter, respectively. Similar emission rates were determined found when the cattle were treated as a herd. Forage quality, how much cows ate and whether the cows had calves or were pregnant determined how much methane the cows produced. These results increase the understanding of how much methane grazing cows produce. Regulators can use these results to improve inventory estimates. Scientists can use the results to check computer programs that predict methane emissions.

Technical Abstract: Methane is a greenhouse gas that contributes to global warming and climate change. Cattle produce methane as a natural byproduct of digestion but measuring this enteric methane that grazing cattle emit is challenging. A team of USDA-ARS scientists in Bushland, Texas, Woodward, Oklahoma and El Reno, Oklahoma studied the enteric methane emitted by grazing beef cows during one to two week-long campaigns during three seasons of the annual grazing cycle – summer, autumn and winter. They used three different methods to measure enteric methane. One method tracked the location of grazing cows with satellite location devices and used open path lasers that are sensitive to methane to measure methane concentration upwind and downwind of the cow herd. We also measured the stability and turbulence of the air. We then ran these measurements through a computer program that can simulate the movement in the air of methane from the cows and calculates how much methane the cattle are emitting. Another method used a device much like a breathalyzer for cattle that measured methane emitted from the mouths of individual cows. A third method measured the actual fluxes of methane upwind and downwind from the herd and used a ratio technique to calculate the herd methane emission. On average, methane emission rate was 0.34, 0.27 and 0.29 kilograms per cow per day during summer, autumn and winter, respectively. Similar values were found when the cattle were treated as a group source. Important factors contributing to enteric methane emissions of the beef cows were the interactions of forage quality and intake, and the physiological state of cows determined by lactation, and early or late pregnancy. These results can be used to improve inventory estimates, check models that predict methane emissions and help us better understand the role of methane in the beef production chain.