Influence of lignin on digestibility of forage cell wall material

One-hundred-ninety-four grass samples, representing eight species, were used to determine the relationships of in vitro forage dry matter, cell wall, hemicellulose and cellulose digestibilities with lignin concentration. Linear regressions indicated that dry matter digestion was inhibited to a lesser degree (P less than .05) by lignin concentration than was cell wall digestion. Results for linear regressions of hemicellulose and cellulose digestibilities as functions of lignin concentration showed a greater (P less than .05) effect of lignin on cellulose digestion. Smooth bromegrass and switchgrass were collected at both Clay Center and Mead, NE; for all digestibility measures, the Clay Center samples gave stronger (P less than .05) negative correlations with lignin. A comparison of linear and curvilinear models indicated that, for all digestion measurements, the curvilinear model was a better (P less than .05) description of relationships with lignin concentration. For all digestibility measures, lignin's inhibiting effect declined at higher lignin concentrations. The curvilinear models did not show significant differences among the digestibility measures for effect of lignin. The demonstration that the forage digestibility response to lignin's inhibitory effect is curvilinear in nature suggests that the mechanism of lignin's inhibition is complex.