The digestibility of wheat straw treated with sulphur dioxide

Abstract

SummaryTwo digestion trials were performed with sheep in order to assess the effect of the sulphur dioxide treatment on the digestibility of wheat straw in vivo. In the first trial, untreated and SO2-treated straw served as the major components of the diets. Sulphur dioxide partly solubilized the cell wall (CW) material of the straw, decreasing its content from 78·5 to 55·9%. The digestibility of the residual CW was increased from 49·2 to 77·8%, whereas the digestibility values of the cell-soluble fraction (CS) were unaffected by the treatment: 55·8 and 57·8% for the untreated and treated straw, respectively. Apparent digestibility of the organic matter (OM) was increased by the treatment from 46 to 65%.In the second trial SO2-treated wheat straw was fed together with concentrates at a D.M. ratio of 30/70, and the digestibility of the OM and CW was determined.CW and OM digestibilities of the treated straw were not affected by 70% concentrate in the diet and the respective values were 77·0 and 65·5%, very similar to those found in the first trial. The reason for the in vitro–in vivo discrepancy is discussed.