Cell Wall Lignification and Degradability

This chapter examines some of the observed empirical relationships of lignin concentration and composition with cell wall digestibility. It emphasizes information regarding molecular aspects of cell wall lignification and mechanisms by which these factors may limit bacterial fermentation and enzymatic hydrolysis of forages. For the purposes of this chapter, core lignin is considered to be the phenylpropanoid polymer deposited in the cell wall from polymerization of cinnamyl alcohols during secondary wall thickening. Composition of the core lignin polymer has been discussed as a factor which influences degradability of cell wall polysaccharides. Pyrolysis is a methodology that is currently seeing increased use for analysis of lignin structure in forages. Inferences regarding relationships of lignification to cell wall degradability drawn from data such as presented in the preceding section must be made cautiously because cell wall composition data result from analysis of total plant herbage.