<i>In vitro</i> evaluation of mixed silage of <i>Pennisetum purpureum</i> and orange fleshed sweet potato vines

Abstract

The study was aimed at determining the in vitro nutritive value of mixed silages of pennisetum purpureum and orange-fleshed sweet potato vines and evaluating their potential of being a new feed resource for ruminants during the dry season. Pennisetum purpureum (Pp) and orange-fleshed sweet potato vines (OFPV) were ensiled in experimental silos bottles after wilting for 24 hours in the following proportions viz:100%Pp (T1), 75%Pp +25%OFPV (T2), 50%Pp +50%OFPV (T3), 25% Pp +75% OFPV (T4) and 100% OFPV (T5). Each treatment was replicated ten (10) times and was kept for 14 and 28 days in the laboratory at a room temperature (20 – 25°C). The chemical composition of the silage at 14 and 28 days was determined. In vitro gas production of the silages was carried out for 48 hours. In vitro fermentation kinetics and gas production parameters of the silages were also estimated. Results revealed that ensiling periods had significant (p<0.05) effect on the dry matter (DM), crude protein (CP), neutral detergent fibre (NDF) and acid detergent fibre (ADF) contents of the silages. Silage of 28 days had highest CP (13.45%) and lowest NDF and ADF contents (40.10 and 25.48% respectively). Silage containing 100% OFPV recorded highest (p<0.05) crude protein (15.95%), ash (15.81%) and lowest NDF (32.25%) and ADF (22.50%) contents. Gas production was lowest (p<0.05) in T1 at all incubation periods, and it increases with inclusion of OFPV, T5 had significant (p<0.05) highest gas production. Least gas production was observed in T1 at 42 and 48 hours incubation period (15.17 and 17.17 mL/200mg DM respectively). Silage of 28 days had the best potential gas production (37.51 mL). Fractional rate of gas production was higher in 28 days silage (0.06mL/hr), T3 (0.05mL/hr), T4 (0.05mL/hr) and T5 (0.06mL/hr) while lag phase was lowest in these silages. In vitro dry matter digestibility (IVDMD), metabolisable energy (ME) and short chain fatty acids (SCFA) were greater in silage of 28 days (63.73%, 5.01MJ/Kg DM and 0.02mL) with least percentage methane production (33.34%). Also, IVDMD, in vitro organic matter digestibility (OMD), ME, and SCFA increased as level of OFPV in the silages increases with T5 having the highest values for these parameters. Percentage methane production was least (p < 0.05) in T5 (26.55%). It can therefore be concluded that Pennisetum purpureum be supplemented with OFPV up to 75% and ensiled for 28 days or beyond to produce better quality feed resource for ruminants during the dry season. Ensiling 100% OFPV is also highly recommended as it exhibited the best nutritive potential.

Keywords: Pennisetum purpureum, potato vines, silage, nutritive value, ruminant nutrition