SO 2-treated straw as a silage additive: The participation of soluble and cell wall monosaccharide residues in lucerne silage fermentation

Abstract

The participation of neutral detergent (ND)-soluble and cell wall (CW) monosaccharide residues in the fermentation of silages made of lucerne + wheat straw was studied in 2-l laboratory glass silos. The treatments consisted of: (a) lucerne wilted to 30% dry matter (DM) prior to ensilage (WL); (b) fresh lucerne + untreated wheat straw at a ratio of 60 40 on a DM basis (L + WS); (c) fresh lucerne + SO 2-treated wheat straw at the same ratio (L + 40%TWS); (d) fresh lucerne + SO 2-treated wheat straw at a ratio of 50 50 on a DM basis (L + 50%TWS). Silos were opened after 90 days of fermentation and silages were analyzed. ND-soluble glucose was extensively or completely fermented in the four silages, whereas the ND-soluble uronic acid (pectin) was hardly affected after 90 days of fermentation. The highest recoveries of ND-soluble sugar residues were in the L + 50%TWS silage. CW glucose and xylose did not participate in silage fermentation, but the minor CW sugars (arabinose, galactose and mannose) were slightly degraded in the L + WS and L + 50%TWS silages. The results indicate that the level of inclusion of SO 2-treated wheat straw will determine whether the source material will be preserved as a result of direct acidification of the HSO 3 − residues present in the TWS, or as a consequence of normal fermentation of the CW-derived soluble sugars contributed by the TWS.