RELATIONSHIP OF LIGNIN AND ESTERIFIED PHENOLICS TO FERMENTATION OF SMOOTH BROMEGRASS FIBER

The importance of concentration and composition of lignin and esterified phenolics in forage cell walls was investigated relative to limitation of fibre fermentation. Smooth bromegrass (Bromus inermis Leyss.) leaf and stem tissues were analyzed for in vitro fermentability of detergent fibre fractions. The smooth bromegrass samples represented nine genotypes selected for high in vitro dry matter disappearance (IVDMD) and nine genotypes selected for low IVDMD. Lignin was an important predictor of fibre fermentation for stems but not for leaves. The relationships of stem neutral detergent fibre and hemicellulose, but not cellulose, fermentability to lignin concentration were different between the high and low IVDMD genotype groups. Nitrobenzene oxidation products were negatively correlated with leaf blade fibre fermentation. Stepwise multiple regression analysis, within IVDMD genotype groups, showed no relationship between fibre fermentation and lignin/phenolic measures for leaves, and primarily a lignin concentration effect in high IVDMD stems. Major differences exist in the importance of lignin concentration, lignin composition, and esterified phenolics concentrations to fibre fermentability of smooth bromegrass genotypes selected for divergent IVDMD.