Digestibility of Forage Hemicellulose and Pectin by Rumen Bacteria in Vitro and the Effect of Lignification Thereon

Summary Four maturity stages of timothy, three of alfalfa, and two of orchard grass were used as substrates to study the rate and extent of hemicellulose fermentation by rumen bacteria in vitro. In all cases, hemicellulose fermentation decreased as the plant matured. When the forage particle size was markedly reduced by ball-milling, an attempt to remove any barrier type of inhibition by lignin, the extent of hemicellulose fermentation increased. This increase became larger with advancing maturity of the forage. The rate and extent of pectin digestion were estimated with three stages of alfalfa. As with the hemicellulose, both the rate and extent of pectin fermentation decreased as the alfalfa matured and the effect of maturity ivas lessened considerably after reduction of the alfalfa particle size by ball-milling. The experimental evidence presented in this paper indicates that both hemicellulose and pectin digestion are influenced by the maturity of the forage, and suggests that this effect is the result of lignin forming a physical barrier between the plant hemicellulose or pectin and the rumen bacteria.