Abstract
Digestibility of total and cell wall monosaccharides was studied in sheep with ruminal and duodenal cannulae and fed three wheat straw-based diets: untreated, treated with SO2, treated with SO2 plus cellulase and a fourth diet, which was barley-based. In untreated straw, 90% of total monosaccharides are cell wall bound. Sulfur dioxide treatment solubilized mainly the matrix sugars, reducing their content from 22.1 to 9.76 g/100 g DM in straw. The combined treatment (SO2 plus cellulase) solubilized most of the cell wall sugars so that the residual cell wall contained only 31% of the total sugars originally present. Treatments increased total monosaccharide digestibility from 63 to 90% and of cell wall monosaccharides from 58 to 84 and 88%. The proportion of digestible monosaccharides degraded in the rumen was increased up to 95% by the treatments. Total monosaccharide digestibility was similar in both treated straws, but degradation of the residual cell wall monosaccharides was somewhat lower in the combined treatment compared with the SO2-treated straw.

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