The use of nitrogen-15 labeling for the assessment of leguminous protein digestibility

This study evaluated the digestibility of leguminous protein labeled with 15N, by using nitrogen balance and quantitation of fecal endogenous nitrogen (FEN), determined by isotopic dilution, in order to correct apparent values. Seeds of common beans, cowpea and common pea labeled with 1.000 atoms% of 15N-excess were used as protein sources in diets for 60 male Wistar rats, during a 6-day assay. The real digestibility values obtained with FEN were 77.6, 84.4, and 86.3% for common beans, cowpea and common pea, respectively. They were higher and statistically different (p < 0.05) than true digestibility values, corrected by non-protein diet. FEN showed a direct, moderate and positive relation with weight of dry matter eaten, initial body weight, weight gain and weight of dry matter of feces, the latter showing the highest correlation, with a coefficient r = 0.8930 at 1% level.