Effects of sucrose, glucose, molasses and cellulase on fermentation quality and in vitro gas production of king grass silage

In order to improve silage quality of king grass (Pennisetum purpureum Schumacher × Penicillium glaucum (Linnaeus) R. Brown) in high moisture environment of tropical area, the effects of sucrose, glucose, molasses and cellulase on fermentation quality and in vitro gas production of king grass silage were studied in Hainan, China. The king grass materials were freshly cut at vegetative stage. Silage was prepared by using a small-scale silage fermentation system, sucrose (SU, 2%), glucose (GL, 2%), molasses (MO, 2%) and cellulase (CE, 0.02%) were used as silage additives (on a fresh matter basis), their treatments were designed as (1) Control (without additives), (2) CE, (3) SU, (4) GL, (5) MO, (6) SU + CE, (7) GL + CE, and (8) MO + CE. These silos were kept at room temperature (25-30 °C), and the silage qualities were analyzed after 30 days of fermentation. The moisture of material was 82.43%; their crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were 8.27, 65.39 and 46.18% on a dry matter basis, respectively. Silages treated with SU, GL and MO were well preserved with significantly (P<0.05) higher lactic acid content, but significantly (P<0.05) lower pH value, and butyric acid and ammonia-N contents compared with control. In addition, MO treatment resulted in better fermentation quality than other single treatments. Silage treated with mixtures of SU + CE, GL + CE and MO + CE increased lactic acid levels compared with control and single treatments, but did not significantly improved the fermentation quality. All additive treatments affected the chemical composition, increased the CP content, decreased the NDF and ADF contents (P<0.05), and enhanced the in vitro dry matter digestibility and metabolizable energy as estimated from in vitro gas production. When the fermentation quality, chemical composition and in vitro rumen fermentation characteristics were considered, the single treatment with carbohydrate or cellulase resulted in high quality of king grass silage, with MO having the best effect.