Washing and filtration of wheat straw treated with sodium hydroxide alone or with hydrogen peroxide to modify cell wall composition and in vitro digestibility

Abstract

Summary. This study compared the effect of different levels (24–160 g/kg DM) of NaOH alone or in combination with 2 levels (130 or 260 g/kg straw DM) of H₂O₂ (alkaline hydrogen peroxide, AHP) in improving in vitro dry matter digestibility of wheat straw. The study also examined the role of filtration or a water wash of straws treated at a regulated pH (± s.d.) of 11.5 ± 0.2 to maximise the effects of NaOH and AHP on in vitro dry matter digestibility. The experiment was a 3 × 2 × 3 factorial design, replicated twice, and included 3 straw groups (pH-control, NaOH-control, AHP), each treated with 2 volumes of chemical solutions (high, 26 L/kg DM containing 48 or 160 g NaOH alone or 160 g NaOH plus 260 g H₂O₂ ; low, 13 L/kg DM containing 24 or 80 g NaOH alone or 80 g NaOH plus 130 g H₂O₂ ) and each was subdivided into 3 groups for storage (unfiltered, filtered, washed). Both NaOH-control and AHP reduced (P<0.001) neutral detergent fibre content and increased (P<0.001) in vitro dry matter digestibility of straw compared with pH-control. However, AHP was more effective (P<0.001) in reducing neutral detergent fibre and increasing in vitro dry matter digestibility of straw compared with NaOH alone. Filtration and washing of treated straws increased (P<0.001) neutral detergent fibre and reduced (P<0.001) in vitro dry matter digestibility compared with unfiltered samples of treated straws. High volumes of chemicals were more effective (P<0.001) in reducing neutral detergent fibre content and improving in vitro dry matter digestibility of straws compared with those treated with low volumes of chemicals. While regulation of pH around 11.5 was effective in reducing neutral detergent fibre and enhancing in vitro dry matter digestibility the use of filtration or a water wash of straws following chemical treatments is not recommended.