Efficacy of a Wavelength-Scanned Cavity Ring-Down Spectroscopic Technique in Estimating Enteric Methane Emissions in Ruminants

Abstract

We report a fast and reliable method of estimating methane (CH 4 ) production from livestock based on direct wavelength-scanned cavity ring-down spectroscopic (CRDS) measurements of CH 4 and carbon dioxide (CO 2 ) dry mixing ratios in a feedlot located at the Hyder-Burks Pavilion Farm at Tennessee Tech University. Simultaneous measurements of CO 2 and CH 4 concentrations from cattle breath enables a direct estimation of the proportion of carbon that is not metabolized to CO 2 but excreted as CH 4 using the CH 4 :CO 2 ratio and the CO 2 from the breath as a tracer gas. A CH 4 :CO 2 ratio of 0.053 ± 0.003 yields an estimated CH 4 production of 243 ± 14 L/cattle/day, and 299 ± 17 L/cattle/ day for cattle with an average body weight of 400 and 680 kg, respectively. The enteric CH 4 emission factor calculated on the basis of the CH 4 :CO 2 ratio allows us to estimate an enteric CH 4 emission of 117 ± 7 Gg yr −1 and 1.43 ± 0.08 Gg yr −1 for the state of Tennessee and Putnam County, respectively.