Lignin Composition and In Vitro Digestibility of Feeds

Fibrous feeds were subjected to nitrobenzene oxidation to examine the effects of lignin composition on feed digestibility. Data from nitrobenzene oxidations, fiber analyses and in vitro digestiblity determinations performed on 15 feedstuffs were examined by regression analysis. The best single predictors of cell wall or dry matter digestibility for all feeds were found to be acid detergent fiber (ADF) (R2 of .71, P<.001 and .82, P<.001) and the percentage of vanillin in lignin oxidation products (R2 of .54, P<.002 and .52, P<.002). With multiple lignin components, lignin, composition was a better predictor of digestibility (R2 ≅ .91, P<.001) than combinations of fiber variables (R2 ≅.78, P< .002). Best models for digestibility included fiber and lignin composition data. In a second series of experiments, seven feeds were subjected to the nitrobenzene oxidation procedure under varying conditions of duration and temperature. Except for peanut hulls, the percentages of various products were dependent on the conditions of oxidation. Comparisons of lignin fractions between temperatures of oxidation of 120 and 160 C and possibly at 160 and 170 C appear useful in predicting digestibility.