In the presentpaper the chemical composition and digestibility of several Brachiaria brizanthaand Brachiaria humidicola fractions were determined after 70 days ofgrowth. The experimental design was completely randomized with five replicationsfor each specie. According to the position, the harvested plants were subdividedinto top, median and bottom fractions for leaves and median and basal fractionsfor stems. The concentration of neutral detergent fiber (NDF), crude protein(CP), lignin, p_coumaric acid, ferulic acid, neutral sugars (glucose, xyloseand arabinose) and in situ digestibility with 48-hour rumen digestionwere determined. The several fractions of species studied showed different chemicalcomposition, whose effects were observed in digestibility. B. brizantharecorded greater NDF concentration in stems and CP in leaves. This resultedin higher digestibility coefficients compared to B. humidicola. The digestibilitydifferences between stem and leaves and in older fractions may be related tothe type of lignin condensation present in tissues. The evidences found in p_coumaricand ferulic acid rates and concentrations suggest this association. The fenolicacid concentration was better related to dry matter digestibility, whereas ligninwith NDF digestibility. This analysis may constitute an important tool to evaluatelignin condensation in cell wall of different forages. The neutral sugars showedno definite deposition pattern in a varied of tissues. Arabinose was the onlysugar associated to dry matter digestibility and fenolic acid concentration.
