Lignin as a Marker in Digestion Studies: a Review

Although lignin has been used extensively as an internal marker in digestion studies, data indicate that problems exist in both fecal recovery and quantification of this cell wall component. Digestibilities of lignin have been reported for diets ranging in composition from 100% forage to 10% forage-90% concentrate. The greatest apparent digestion of lignin appears to occur in the rumen, but modification of lignin structure has also been reported as a result of activities occurring in the lower gut. Certain data suggest that microorganisms of the gastrointestinal tract may be responsible for degradation and(or) modification of lignin structure. Analytical techniques for quantification of lignin are empirical in nature and differ significantly in their estimation of plant lignin content. Method of analysis also affects comparisons of lignin digestion among feeds and within sections of the gut. Lignin should be used as a marker only when evidence exists that fecal recoveries are high.