Effect of Inclusion of Protein-rich Forages on Quality of Napier Grass Silage

Abstract

In order to study the effect of inclusion of protein rich forages (PRF) and molasses on chemical composition, metabolisable energy (ME) content, voluntary' intake, in vivo and in vitro digestibility of Napier grass silage, four experiments were performed. In experiment one, Napier grass harv ested at three stages of growth (4, 8 and 12 weeks from the last cutting) was ensiled singly, or mixed with protein rich forage (PRF) Ixiblab purpureus. Mucuna pruriens, Crotalaria ochroleuca and Leucaena leucocephala (20%) for 30, 60 and 90 days in miniature polythene silos. Each of the silages was made with and without 3% molasses. Inclusion of molasses, with or without PRF, significantly (p<0.01) lowered silage pH over the storage period for all Napier grass ages. Inclusion of PRF except Leucaena increased the ammonia nitrogen of the silage (P<0.05). Addition of molasses reduced ammonia nitrogen content of both non-supplemented and PRF-Napier grass silages. In experiment two, the in vitro fermentation kinetics of the silages and pre-ensiled forage were determined using a gas production technique. The rate of gas production for the preensiled PRFs and PRF-Napier grass silages were higher (P<0.()5) than for pre-ensiled Napier grass and non-supplemented Napier grass silage. The stage of growth (8 and 12 weeks) of Napier grass did not affect the rate of gas production or the cumulative gas volume of the silages. Within the PRFs, Ixiblab had the highest (10.4%/hour) and Leucaena the lowest (7.3%/hour) rate of gas production. Inclusion of molasses increased (P<0.()()1) the rate of gas production and ME for both Napier and Napier-PRF silages irrespective of age of Napier grass. In experiment three, Napier grass was ensiled singly (NG) or in combination with Mucuna pruriens (NGM) and Dolichos lablab (NGL) in pit silos. Molasses was included at 3% in all the silages. In sheep, the voluntary' dry matter intakes were 74, 81 and 83 g/kgLW0 75 for the NG, NGM and NGL silages respectively. Inclusion of legumes did not affect the voluntary' intakes of DM and OM but increased (P<0.05) the CP intake (145, 183 and 183 g/animal/dav for NG, NGL and NGM respectively. PRF inclusion did not XVII affect the digestibility of dry matter but increased the digestible crude protein (g/dav). The ME calculated both from in vivo digestible nutrients and in vitro gas production was higher (P<0.05) for NGL (8.0 and 7.7) and lower for NGM (7.6 and 7.2) than the NG (7.8 and 7.4 MJkg"1 DM). Inclusion of PRF increased the nitrogen retained from 4.46 g/day for NG to 7.74 and 6.30 for NGL and NGM respectively. The ratio of nitrogen to ME was higher in the supplemented silage (2.3 and 2.4 for NGL and NGM respectively) compared to 2.0 gMJ'1 for NG. In experiment four, the effects of tannins in PRFs (Mucuna pruriens, Dolichos loblab, Crotalaria ochroleuca and Leucaena leucocephala, Acacia tortilis, Acacia angustissima. Moms alba, Calliandra calothyrsus) on in vitro fermentation were investigated. Polyethylene glycol (PEG, MW 6000) was used as a tannin binder. Inclusion of PEG increased (P0.001) the gas production by 23, 54, 112 and 475% for Leucaena leucocephala, Acacia tortilis, Calliandra calothyrsus and Acacia angustissima respectively. Addition of PEG increased (P<0.001) the total volatile fatty acids, acetic, propionic, butyric, isobutvric and isovaleric acids for Leucaena leucocephala, Calliandra calothyrsus and Acacia angustissima. There were minimal gas production increases for Mucuna pruriens, La blab purpureus, Crotalaria ochroleuca and Morus alba on incubation with PEG. Gas production from Napier grass was reduced (P<0.05) by inclusion of Acacia angustissima. Calliandra calothyrsus and Leucaena leucocephala. This effect was dose dependent and was reversed by inclusion of PEG. In vitro nitrogen degradability and microbial nitrogen uptake were increased (P<0.001) by the inclusion of PEG.