PETERSON, M.R.*; HATCH, K.A.; Brigham Young University; Brigham Young University: Validation of the two-endpoint mixing model to determine diet composition from ¹³C/¹²C of breath

Stable isotope ratios of carbon are frequently used to determine dietary contribution of two isotopically distinct food sources. While the ¹³C/¹²C ratios of specific tissues are often used for such estimates, several studies have indicated that the δ¹³C value of exhaled CO₂ more closely represents that of diet than do the δ¹³C values of most tissues. While a two-endpoint mixing model is usually used to estimate dietary contribution of isotopically different food sources, the assumptions underlying that model and the ability of that model to accurately determine dietary contribution frequently go untested. We tested the ability of the two-endpoint mixing model to accurately determine the percent of C₃ and C₄ grains eaten by white-winged doves (Zenaida asiatica) from the δ¹³C value of exhaled CO₂. We used six white winged doves. They were fed varied weights of C₃ (wheat, Triticum aestivum) and C₄ (millet, Panicum miliaceum subsp. miliaceum) grains for 30 minutes daily. The remaining grain was separated and weighed to determine the amount of each grain that was eaten. We took breath samples 3, 5, and 7 hours after feeding. We then compared the wheat/millet ratio eaten by the doves as determined by weight to the wheat/millet ratio eaten by the doves as determined by the two-point mixing model.