Carbon isotopes in exhaled breath track metabolic substrates in brown bears (Ursus arctos)

• Published in: Journal of Mammalogy
• Main Authors: Whiteman, John P., Greller, Katie A., Harlow, Henry J., Felicetti, Laura A., Rode, Karyn D., Ben-David, Merav
• Format: Text
• Language: English
• Published: Oxford University Press 2012
• Subjects: Special Feature; Ursus arctos
• Online Access: http://jmammal.oxfordjournals.org/cgi/content/short/93/2/413; https://doi.org/10.1644/11-MAMM-S-178.1

Dietary carbon is oxidized and exhaled as CO 2 , thus δ13C breath values can provide information on diet and substrate use for energy. However, physiological phenomena such as fat deposition and fasting can alter values of δ13C breath such that interpretation of source contributions may be unclear. Consequently, before application to free-ranging animals, inferences about feeding and nutritional states based on δ13C breath should be validated with controlled experiments using captive individuals. Here, we report δ13C breath values for 4 captive brown bears ( Ursus arctos ) under different conditions: the bears were 1st given a diet containing carbohydrate, lipid, and protein; they were then switched to a carbohydrate-free diet consisting of salmon and fish oil; and finally they were placed on a fast leading to winter hibernation. Following the switch to the carbohydrate-free diet, values of δ13C breath and δ13C plasma suggested that although oxidation included a substantial portion of dietary proteins, dietary lipids were preferentially utilized. After the onset of fasting, δ13C breath values did not change, possibly because of selective mobilization of endogenous fatty acids accreted by bears while consuming the experimental diet. Examination of our data suggests that because CO 2 production and exhalation are influenced differentially by fasting state and diet composition, additional measurements such as respiratory exchange ratio should be used to aid interpretation of carbon isotope analysis of breath.