CH4/CO2 Ratios and Carbon Isotope Enrichment Between Diet and Breath in Herbivorous Mammals

Breath and diet samples were collected from 29 taxa of animals at the Zurich and Basel Zoos to characterize the carbon isotope enrichment between breath and diet. Diet samples were measured for delta C-13 and breath samples for CH4/CO2 ratios and for the respired component of delta C-13 using the Keeling plot approach. Different digestive physiologies included coprophagous and non-coprophagous hindgut fermenters, and non-ruminant and ruminant foregut fermenters. Isotope enrichments from diet to breath were 0.8 +/- 0.9 parts per thousand, 3.5 +/- 0.8 parts per thousand, 2.3 +/- 0.4 parts per thousand, and 4.1 +/- 1.0 parts per thousand, respectively. CH4/CO2 ratios were strongly correlated with isotope enrichments for both hindgut and foregut digestive strategies, although CH4 production was not the sole reason for isotope enrichment. Average CH4/CO2 ratios per taxon ranged over several orders of magnitude from 10(-5) to 10(-1). The isotope enrichment values for diet-breath can be used to further estimate the isotope enrichment from diet-enamel because Passey et al. (2005b) found a nearly constant isotope enrichment for breath-enamel for diverse mammalian taxa. The understanding of isotope enrichment factors from diet to breath and diet to enamel will have important applications in the field of animal physiology, and possibly also for wildlife ecology and paleontology.

Automated summary

This study collected breath and diet samples from 29 animal taxa from Zurich and Basel Zoos to investigate carbon isotope enrichment. Different digestive physiologies were found to impact isotope enrichments, and CH4/CO2 ratios were correlated with these enrichments. The findings have implications for animal physiology, wildlife ecology, and paleontology.