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Evaluation of the GreenFeed method relative to the United States Pharmacopeia methodology validation guidelines.

S. Zimmerman




Evaluation of the GreenFeed method relative to the United States Pharmacopeia methodology validation guidelines.
B. Garcia1, S. Zimmerman*1, K. Schaefer2. 1C-Lock Inc Rapid City, SD, 2DSM Nutritional Products Basel, Switzerland.

The GreenFeed (GF) gas flux (mass flowrate) measurement system is a non-invasive means of measuring enteric methane (CH4) from ruminant animals. GF has been used for several purposes, including evaluating the effectiveness of feed additives [KM1] in reducing enteric CH4 emissions. This study evaluated GF parameters using the United States Pharmacopeia < 1033 > �2.4 guidelines (USP) for instrument methodologies. Per USP guidelines, concentration measurements were evaluated using 5 certified CH4 concentration mixtures (103.7—2104 ppm) in 3 replicates passed through the GF system. In addition, CH4 flux measurements were evaluated by releasing gravimetrically measured ‘pulses' of CH4 at 5 different fluxes (70.7—509.7 g/d), with at least 3 replicates each, at a range of temperatures (4—29�C) and pressures (912—927 mbar) into the GF intake manifold. The tests were repeated with 2 unique GF machines to measure between unit variability. The USP requires repeatability and precision analysis using ‘Intermediate Precision' (IP) reported as %Geometric Coefficient of Variation, using mixed linear models (MLM). Significance of random effects was determined by ratio tests between a model with a given random effect and a model without. Singular (zero) variance estimates were removed. The MLM were computed using the ‘lmer' function of the ‘lme4' library for the R platform, while ratio tests used the ‘anova' function. CH4 flux estimates had an IP of 6%, while concentration estimates had an IP of 2%. The GF measurements were found to be highly correlated to certified concentration standards and gravimetric fluxes (0.9993, 0.9972). The GF system estimated CH4 fluxes with 1.92% average relative bias. Concentration estimates had 0.15% average relative bias. Concentration variance estimates were non-singular for the pressure of the environment, while flux variance estimates were non-singular for pressure and replicate. Temperature, and the GF unit performing the measurement were singular effects. In summary, GF produces repeatable and accurate emissions measurements compared with gravimetric measurements or certified concentration standards.

Keywords: methane, measurement, emissions.