The Chemical Composition, in Vitro Nutrient Degradation and Methane Gas Production of Tropical Grasses Preserved with Silage and Hay Methods

Abstract

Six grass species (Pennisetum purpureum, Pennisetum purpureophoides, Sorghum sudanense, Brachiaria brizantha, Imperata cylindrica, and Panicum maximum) were harvested at 49 days and preserved as silage or as hay. Samples of silage and hay were evaluated by an in vitro gas production and in vitro nutrient degradability. Total gas production at 24 and 48 h as well as CH4 were higher (P<0.01) in silage than in hay. Brachiaria brizantha had the highest (P<0.01) gas production compared to other species, whereas P. purpureum had the highest CH4 production (mM/g organic matter degraded). Dry matter (DM) and organic matter (OM) degradations were higher (P<0.01) in silage than hay. When compared with hay, silage had higher (P<0.01) ammonia-N concentration (20.3 vs. 10.6 mg/100 ml) and higher (P<0.05) butyric acid concentration (7.9 vs. 7.0 mM). Non-fi ber carbohydrate (NFC) and crude protein contents were positively correlated with gas production (r = 0.51; P<0.05) and CH4 production (r = 0.64; P<0.01) at 48 h of in vitro incubation. However total gas and CH4 productions were negatively correlated with neutral detergent fi ber (NDF) content. There were positive correlation between DM (r = 0.90; P<0.01), OM (r = 0.93; P<0.01), and NDF (r = 0.84; P<0.01) degradations and gas production.