PODLESAK, D.W.*; MCWILLIAMS, S.R.; University of Rhode Island, Kingston: Using stable isotopes to investigate the effects of diet quality on metabolic routing of dietary nutrients in birds

Stable isotopes can be used to quantify the magnitude of metabolic routing of dietary nutrients in birds fed diets of different qualities. We tested two hypotheses: birds fed nutritionally adequate diets primarily route dietary macronutrients such as proteins into the same macronutrient types in their tissues. In contrast, birds fed nutritionally inadequate diets must route carbon from nonprotein dietary sources into protein synthesis. Thus, delta C of proteinaceous tissue such as hematocrit should be most similar to delta C of dietary protein when diets are nutritionally adequate. We fed 32 yellow-rumped warblers (Dendroica coronata) a semi-synthetic 25% protein diet composed of all C3 ingredients. After 2.5 months, birds were assigned to 1 of 5 diets: Diet 1=25% protein, all C4; Diet 2=25%C4 protein, C3 carbohydrate and lipid; Diet 3=25%C3 protein, C4 carbohydrate and lipid; Diet 4=4%C4 protein, C3 carbohydrate and lipid; Diet 5=4%C3 protein, C4 carbohydrate and lipid. After 15 days, delta C of hematocrit from birds switched to Diet 1 changed 5.05‰, Diet 2 changed 2.66‰, Diet 3 changed 1.49‰, Diet 4 changed 1.39‰, and Diet 5 changed 2.63‰. After 15 days, delta C of plasma from birds switched to Diet 1 changed 8.40‰, Diet 2 changed 3.19‰, Diet 3 changed 6.39‰, Diet 4 changed 1.52‰, and Diet 5 changed 7.84‰. Thus, dietary protein was primarily routed to proteinaceous tissue for birds fed nutritionally adequate diets (Diets 1,2,3), whereas birds fed nutritionally inadequate diets (Diets 4,5) routed carbon from nonprotein dietary sources to proteinaceous tissue. These results demonstrate that dietary routing in birds depends on the delta C signature of dietary macronutrients as well as the carbohydrate and lipid composition of the diet.