[Show abstract][Hide abstract] ABSTRACT: We compared d13C and d15N ratios of barn-raised and free-range chickens to determine if differences in their diets were reflected in the stable isotope composition of their tissues. We conducted a 120-day feeding trial with Caipirinha birds fed a corn–soybean based diet, milled-corn diet and free-range diet. Additionally,
we analysed the stable isotope composition of barn-raised chickens bought in grocery stores and free-range homegrown chickens. In the feeding trials, the d13C and d15N values of the barn-raised corn–soybean-fed Caipirinha chickens did not change with age, and their stable isotope composition reflected the composition of their diet. The d13C and d15N values of barn-raised corn-fed and free-range Caipirinha chickens changed with age toward a diet reflecting a predominance of C4 carbon. The main difference between the free-range and the barn-raised chickens was the significantly higher d15N of the former in relation to the latter, probably due to ingestion of animal protein.