Performance of a dispersion model to estimate methane loss from cattle in pens
Received for publication December 29, 2008. Accurate measurements of enteric methane (CH4) emissions from cattle (Bos taurus) are necessary to improve emission coefficients used in national emissions inventories, and to evaluate mitigation strategies. Our study was conducted to evaluate a novel approach that allowed near continuous CH4 measurement from beef cattle confined in pens. The backward Lagrangian Stochastic (bLS) dispersion technique was used in conjunction with global position system (GPS) information from individual animals, to evaluate CH4 emissions from pens of cattle. The dispersion technique was compared to estimates of CH4 production using the SF6 tracer technique. Sixty growing beef cattle were fed a diet containing 60% barley silage (dry matter basis) supplemented with either barley (Hordeum vulgare L.) grain or corn (Zea mays L.) distillers dried grains. The results show that daily CH4 emissions were about 7% lower for the dispersion technique than for the tracer technique (185 vs. 199 g CH4 animal–1 d–1). The precision of the dispersion technique, relative to the SF6 tracer technique, expressed by the Pearson coefficient was 0.76; the relative accuracy given by the concordance coefficient was 0.69. The bLS dispersion technique was able to detect differences (P < 0.05) due to diet and has the added advantage of measuring the pattern of CH4 production during the 24-h period, with emissions ranging from 161 to 279 g CH4 animal–1 d–1. Configuring the cattle as point sources resulted in more accurate CH4 emissions than assuming a uniform area release from the pen surface. The results indicate that the bLS dispersion technique using cattle as point sources can be used to accurately measure enteric CH4 from cattle and to evaluate the impact of dietary mitigation strategies.