Characterisation of lignins in straw, rumen liquor and faeces of sheep fed untreated and SO2-treated wheat straw

Abstract Sheep were fed two rations based on untreated (WS) and SO 2 -treated (SO 2 -WS) wheat straw and the lignins isolated from straws, rumen liquor and faeces underwent high performance size exclusion chromatography (HPSEC). Dioxane lignins (DL) isolated from ball-milled and cellulase pretreated neutral detergent fibre of straws and from their respective faecal materials showed similar molecular weight distribution patterns and similar weight average molecular weight ( MW ) values. Water-soluble lignins (WSL) were isolated from the water extract of the straws and from the liquid phase of their respective rumen liquor and faecal materials. On both rations, rumen WSL were more dispersive and had a higher MW than the WSL isolated from the respective straws. On each of the rations, the DL isolated from the straw and the respective rumen WSL had similar MW values. The major fraction of rumen WSL resided in the molecular weight range 1500-10 000, whereas that of the straw DL resided in the range 10 000–24 000. However, there was a certain degree of overlapping with respect to the HPSEC features, between each of the straw DL and its respective rumen WSL. Molecular weight distribution and MW of rumen and faecal WSL were very similar in the SO 2 -WS ration, indicating little absorption of phenolic material from the intestine of sheep fed this ration.