title: Ruminant methane delta(13C/12C) values: relation to atmospheric methane.
abstract: The delta(13C/12C)--values of methane produced by fistulated steers, dairy cattle, and wethers, and dairy and beef cattle herds show a bimodal distribution that appears to be correlated with the plant type (C3 or C4, that is, producing either a three- or a four-carbon acid in the first step of photosynthesis) consumed by the animals. These results indicate that cattle and sheep, on a global basis, release methane with an average delta(13C/12C) value of -60 and -63 per mil, respectively. Together they are a source of atmospheric methane whose delta(13C/12C) is similar to published values for marsh gas and cannot explain the 20 per mil higher values for atmospheric methane.
mesh_terms: D000818:Animals; D001272:Atmosphere; D002247:Carbon Isotopes; D002417:Cattle / Q000378:metabolism*; D004884:Eructation; D008697:Methane / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D008697:Methane