Differences at the 0.05 level were reported as significant. In order to estimate the turnover rate of breast tissue, we used the following equation: equation(1) δt=δn+(δ0-δn)∗e-(ct)δt=δn+(δ0-δn)∗e-(ct)where
δ is the δ13C or δ15N values of the breast muscle at time t after the diet change; δ0 is the initial δ13C or δ15N values of the breast muscle before the diet change at time t = 28 days; δn is the δ13C or δ15N values of the breast muscle in equilibrium with the new diet; c is the total turnover; and t is the time in days since the start of the new diet ( Hesslein et al., 1993 and Hobson and Clark, 1992). Half-lives (t1/2) of breast muscle were estimated by the following equation: IWR 1 equation(2) t1/2=-ln(2)/ct1/2=-ln(2)/cThe time to reach 99% of the turnover in the tissue 3-Methyladenine manufacturer is given by the following equation: equation(3) t99=ln(0.01)/ct99=ln(0.01)/c The observed temporal change of δ13C and δ15N values after the diet change
followed an exponential model. Accordingly, generated δ13C and δ15N values were adjusted in a non-linear regression equation using the software STATISTICA Version 10. The δ13C values of milled corn used as a diet component in this study were those typical of C4 plants and similar to the average value found for grass samples (Table 2). The diet for barn-raised chickens used in the trials was basically composed of corn and soybean without any kind of animal protein added. Their δ13C values reflect the relative proportion of C3 (soybean) and C4 (corn) plants. The starter diet (given up to 28 days) had a proportion of 65% C4 (corn), while the final diet (given after 28 days) had a proportion of 52% (Table 2). The remaining 35% and 48%, respectively, was composed of C3 (soybean). The δ15N values of our starter
and final diets were lower than the milled corn because the presence of soybean in significant proportions and the absence of animal protein (Table 2). The highest δ15N values were observed in grass and soil samples. Protein tyrosine phosphatase Generally these high values are due to ammonia volatilisation from animal faeces, which is a highly fractionating process, leading to an N-15 enrichment of the substrate (Choi, Ro, & Hobbie, 2003). The average δ13C values of barn-raised corn–soybean-fed Caipirinha chicken diet did not change with chicken ages and was similar to the δ13C of their diet ( Fig. 1). However, we observed variable diet-tissue fractionation during the trial. During the first 28 days, the δ13C of the tissue was lower than the diet and the fractionation was −0.1‰. After the initial period, the δ13C of the tissue became higher than the diet and the fractionation increased to 1‰ at 60 days, decreasing to 0.6‰ at 90 days and increasing again to 1.1‰ at 120 days. The average δ15N of barn-raised corn–soybean-fed Caipirinha chickens did not differ between the 28-day and 60-day old chickens, being similar to the δ15N of their diet.