Carbon isotope ratios in exhaled CO(2) can be used to determine not just present, but also past diets in birds.

We show that an animal's past and present diet can be distinguished through the delta(13)C of exhaled CO(2). The exhaled delta(13)C of 12 pigeons fed solely corn (a C(4) plant) for 30 days was -13.63 per thousand (+/-0.30). We then fed six pigeons wheat (a C(3) plant) and continued to feed the other six corn. After 48 h the exhaled delta(13)C from the corn-fed pigeons was unchanged; that from the wheat-fed pigeons was -20.5 per thousand. We then fasted three of the wheat-fed pigeons for 3 days, after which their exhaled delta(13)C was -14.96 per thousand, while it was -13.57 per thousand in corn-fed pigeons, and -22.22 per thousand in pigeons that continued on wheat. Thus, we could infer diet from the (13)C/(12)C ratios of exhaled CO(2). Significantly, breath samples from fasted pigeons also revealed that they had eaten corn when their lipid stores were formed. We also showed that the change in the (13)C/(12)C of exhaled CO(2) had a half-life of approximately 3.5 h, and a time constant of approximately 6.7 h. Thus one can infer past and present diet from exhaled delta(13)C alone, if the initial breath sample is followed by a fasted breath sample, without harming the animal or having to recapture it successively.

How does time since feeding affect the fuels pigeons use during flight?

Time between meals can vary from multiple hours to days within and among species. We investigated the effects of time since feeding on lipid, protein, and carbohydrate oxidation in flying pigeons (Columba livia) by interpreting changes in blood plasma metabolite concentrations and mass during flight. Five pigeons were flown or rested for 4 h after food deprivations of 2, 12, 24, and 48 h. After flight, blood plasma concentrations of uric acid and beta-hydroxybutyrate were elevated over control and preflight values, indicating elevated protein and lipid catabolism during flight. Lipid oxidation, as indicated by changes in beta-hydroxybutyrate concentration, increased more in unfed flying pigeons compared with recently fed flying pigeons and with resting controls. Protein oxidation, as indicated by changes in uric acid concentrations, also positively covaried with feeding time; the covariation was mostly caused by increases in 48-h food-deprived pigeons. Unfed birds lost less mass during a 4-h flight than recently fed birds. We reasoned that recently fed pigeons oxidized more glycogen in flight than pigeons not recently fed; calculated glycogen stores explained 72%-117% of mass loss differences between 2- and 48-h-fed pigeons. Thus, time since feeding was an important determinant of the fuels pigeons used in flight.

Early detection of catabolic state via change in 13C/12C ratios of blood proteins.

We find that induction of catabolic state changes the ratios of carbon 13 to carbon 12 in blood proteins. Diet can be inferred in growing chicks by feather carbon isotope ratios. This suggests an approach for early detection of catabolic state induced in patients with HIV, cancers that induce catabolism, infection onset, sepsis, kidney and liver disease, malnutrition and dietary problems. The technique would also be useful in animal husbandry.