Determination of (13)C/(12)C-Ratios in Rumen Produced Methane and CO(2) of Cows, Sheep and Camels

Abstract Naturally produced methane shows different δ(13)C-values with respect to its origin, e.g., geological or biological. Methane-production of ruminants is considered to be the dominant source from the animal kingdom. Isotopic values of rumen methane-given in literature-range between -80‰ and -50‰ and are related to feed composition and also sampling techniques. Keeping cows, camels and sheep under identical feed conditions and sampling rumen gases via implanted fistulae we compared δ(PDB) (13)C-values of methane and CO(2) between the species. Referring to mean values obtained from 4 or 5 samples at different times of 11 animals (n = 47) we calculated δ(PDB) (13)C-medians resulting in small but not significant differences within and significant differences between the species for CO(2) and methane. The δ(PDB) (13)C-differences between methane and CO(2) were statistically equal within and also between the species. Therefore a linear regression of methane values on CO(2) is appropriate and leads to: δ(PDB) (13)C(methane)‰ = 1,57 * δ(PDB) (13)C(CO(2))‰-47‰ with a correlation coefficient of r = 0,87.