Effect of Carbohydrate Additives on Fermentation Characteristics, Chemical Composition and Ruminal Degradability of Napier Grass (Pennisetum purpureum) Silage

The objective of the study was to determine the effect of carbohydrate additives on the fermentation characteristics, chemical composition and ruminal degradability of Napier grass silage. Napier grass planted at the School of Agriculture Experimental Farm, University of Venda in 5 x 4 meter plots was irrigated once every week for a period of 12 weeks. After 12 weeks, the Napier freshly cut grass was ensiled with no additive, molasses, maize meal and brown sugar at 10 % fresh weight in a completely randomized design replicated 6 times for 90 d in 1 liter glass jars. After 90 d, silages were determined for fermentation quality and nutritive composition using standard protocols. The DM and CP ruminal degradability was determined in sacco by incubating silage samples in nylon bags (external dimension: 6 × 12 cm, pore size of 46 µm) in the rumen in three Bonsmara steers fitted with rumen cannula for 0, 6, 12, 24, 48, 72, 96 and 120 hours. Parameters to describe the dynamics of ruminal degradability of DM and CP were obtained by fitting the data on the exponential equation p = a + b (1 - e^-ct) using NEWAY computer program, where “a” is the rapid degradable fraction, “b” is the slow degradable fraction, “a+b” is the potential degradability and “c” is the outflow rate. Collected data were subjected to analysis of variance using general linear model procedures of Minitab Statistical package version 17. Molasses treatment had higher (P <0.05) residual water soluble carbohydrates, ash and DM content and lower (P <0.05) ammonium nitrogen and neutral detergent fibre content of silage. In addition, maize meal silage had higher (P <0.05) fat content and lower (P <0.01) acid detergent fibre. However, additives increased (P <0.05) DM disappearance for all incubation hours, and CP disappearance for 48 and 120 incubation hours. As a result, increased (P <0.01) “a”, “b” and “a+b” fractions, and effective degradability at 2, 5 and 8 % outflow rate for DM and also “a+b” (P <0.05) for CP were observed. Therefore, our results suggest that additives were effective in improving the quality of Napier grass silage leading to improved ruminal degradability, with molasses treatment yielding the best silage quality.