The effect of physical and chemical treatments on the degradation of wheat and barley straws by rumen liquor‐pepsin and pepsin‐cellulase systems

Samples of wheat and barley straw, milled through a 1 mm sieve, were ball milled to <0.25 mm as a representative physical treatment, or delignified by the acidchlorite procedure as a representative chemical treatment. The original and treated samples were examined using in‐vitro digestion systems based on rumen liquor‐pepsin and pepsin‐cellulase. The digestibility was determined as well as the extent of digestion of the cellulose, hemicelluloses and lignin. The rumen liquor‐pepsin system was able to digest a greater proportion of the original and treated straws than the pepsin‐cellulase system while ball milling improved the digestibility more than delignification, irrespective of the digestion system. Core lignin was not digested by either system. Ball milling improved the digestibility of the cellulose fraction to a greater extent than the hemicellulose fraction, whereas delignification had a greater effect on hemicellulose digestion than on cellulose digestion. There were also differences in the rate of removal of the different sugar residues present in the hemicellulose fraction.