Digestion of polysaccharide constituents of tropical pasture herbage in the bovine rumen. IV. The hydrolysis of hemicelluloses from spear grass by cell-free enzyme systems from rumen fluid

Hemicelluloses have been isolated from spear grass (Heteropogon contortus), before and after digestion in the rumen, and separated into linear and branched fractions. Similar fractions have also been obtained from a pasture sample and from the faeces fibre of a steer fed on the same pasture. The rates of hydrolysis of all of these hemicellulose fractions have been determined in the presence of extracellular enzymes from rumen fluid and of enzymes liberated by disruption of rumen microorganisms. The oligosaccharide products of such enzymic degradations have been partially identified. The results confirm that the incomplete digestion of hemicelluloses in the rumen is due to physical protection (e.g. by lignin), rather than to structural differences between different components of the hemicelluloses. There is no difference between rates of digestion of branched and linear hemicelluloses, and previous results which indicated such differences were probably caused by presence of a readily digested glucan in linear hemicellulose fractions.