Effects of sugar sources and doses on fermentation dynamics, carbohydrates changes, in vitro digestibility and gas production of rice straw silage

To elucidate the differences of various sugar sources and doses on rice straw silage, the effect of molasses (M, direct substrate) and fibrolytic enzyme (E, indirect substrate) with four doses on fermentation dynamics, carbohydrates and in vitro digestibility was evaluated. Molasses (0, 2, 3 and 4% of fresh weight) or fibrolytic enzyme (0, 0.02, 0.04 and 0.06%) were applied to fresh rice straw ensiling for 3, 6, 9, 15, 30 and 60 days. All additives increased lactic acid content and lactic/acetic acid, reduced pH, NH3-N content of resulting silage (p < .05). The highest lactic acids, residual sugar and fibre degradation were observed in 0.06%E (p < .05). M-treated silage had higher dry matter (DM) content, in vitro digestibility of DM and neutral detergent fibre, and less DM loss, acetic acid, butyric acid and in vitro gas production (GP) than other treatments. Both sugar sources effectively improved fermentation quality. Fibrolytic enzyme induced free sugar release from fibre, especially from hemicellulose, while molasses showed a potential dose effect to decrease ruminal energy waste by increasing digestibility and decreasing GP in vitro. 3%M, 4%M and 0.04%E produced moderate silage based on V-score, and 4%M is recommended for rice straw silage, indicated by intermediate fermentation quality and higher in vitro digestibility.