Size Exclusion Chromatography of Cotton Stalk Lignins Isolated from Rumen Digesta and Feces of Sheep

Sheep were fed two rations based on cotton stalks (CS) and ozonated cotton stalks (OCS). Lignins from these materials and the appropriate rumen liquor and feces were isolated and examined by high-performance size exclusion chromatography (HPSEC). Dioxane lignins (DL) isolated from ball-milled plus cellulase-pretreated neutral detergent-fiber of OCS were more dispersive and had a higher weight-average molecular weight (MWt) than the DL isolated from CS. The carbohydrate content of both CS and OCS DL was about 5%; xylose, uronic acid, and glucose were the major sugars. The patterns of molecular weight distribution of DL in CS and its respective fecal material were similar. This was not the case for OCS, in which the fecal DL was lower in MWt and consisted of a larger proportion of low molecular weight lignins. Water-soluble lignins (WSL) were isolated from the water extract of CS and OCS and from the respective rumen liquor and fecal materials. On both rations, rumen WSL were remarkably more dispersive and had a much higher MWt than the WSL isolated from the respective CS and OCS materials. The proportion of the high molecular weight fractions of WSL was markedly higher for rumen liquor than for feces on both rations. Cell wall degradation in the rumen probably is due to the removal into solution of matrix polymers, rather than monomer degradation