232 In Vitro Digestibility of Dry Matter and Nitrogen of Napier Grass Silage Is Affected By Fertilization with Cow-Dung Bio-Digester Slurry and Fermentable Carbohydrate Additives at Ensiling

Abstract

Abstract The use of silages during the dry season could ameliorate major nutritional constraints in ruminant livestock production in tropical regions. Napier grass (Pennisetum purpureum) is a tropical forage source that is used for silage in South Africa. The present objective was to determine the effects of fertilization with bio-digester slurry (BDS) and of carbohydrate additives [no additive (control), molasses, brown sugar, and maize meal] at ensiling on in vitro digestibility of Napier grass silage. Fresh Napier grass irrigated weekly with either BDS or water was cut after 12 weeks and ensiled for 90 days in 1 liter glass jars in a 2 (control and slurry irrigation) x 4 (no additive, molasses, maize meal and brown sugar) factorial arrangement replicated three times. The nutrient composition was determined using standard protocols. The in vitro digestibility of dry matter (DM) and crude protein (CP) were determined by the three-stage method after incubation in rumen of steers for 12, 24 and 48-hour incubation. The bags containing rumen undegradable residuals (RURs) were removed from the bags, composited by treatment, and ground through a 1 mm sieve. Approximately 1g samples of RURs of each silage sample were placed in a 0.1 N HCl solution adjusted to pH 1.9 with 1 g ℓ-1 of pepsin, and then in pancreatin solution and rinsed with deionized water and dried at 60°C for 48 h. At 24 h incubation, the no BDS, no additive (control) treatment had the least (P < 0.01) DM degradability. As incubation time progressed to 48 h, fertilization with BDS with molasses inclusion increased (P < 0.05) DM disappearance. However, the BDS fertilization and carbohydrate additive interaction had no effect (P > 0.05) on 12 incubation h, and in vitro digestibility after 12, 24 and 48 h of incubation. Fertilization with BDS reduced (P < 0.05) DM digestibility after 48 hours of rumen incubation. Carbohydrate additives increased (P < 0.01) DM disappearance at 12, 24 and 48 rumen incubation h but did not not influence in vitro DM digestibility after 12, 24, and 48 h of rumen incubation. Fertilization with BDS and carbohydrate additives at ensiling interaction had no effect (P > 0.05) on CP degradability at 12, 24, and 48 h of rumen incubation, and in vitro CP digestibility after 12, 24, and 48 h of incubation. Carbohydrate additives increased (P < 0.01) CP disappearance at 12, 24 and 48 rumen incubation h and reduced (P < 0.01) in vitro CP digestibility after 12 h of rumen incubation but did not have an effect (P > 0.05) on in vitro CP digestibility after 24 and 48 h of rumen incubation.