Fermentation kinetics and in vitro digestibility of tropical forages used in sheep and goat production systems in the Caribbean

The in vitro fermentation kinetics and digestibility of six tropical grasses and five multipurpose tree species (MPTs) found in the Caribbean were determined by the current study. The in vitro gas production was measured and fitted to a dual and single pool model to determine the fermentation kinetics of these forages. The average rate of the fast pool (C-1) for grasses was over 20% higher than that of the MPTs. The volume of the fast pool by the dual pool model (V-1) for grasses was 40% lower and the slow pool (V-2) 30% greater than that of the MPTs. There was a strong negative relationship between the fast pool of the dual pool model (V-1) and the neutral detergent fibre (NDF) (r = -0.781) and acid detergent fibre (ADF) (r = -0.655) fractions and a positive relationship between the V-1 and the digestible organic matter in dry matter (DOMD) (r = 0.537). Moringa oleifera was at the higher end of the range for the total gas production by the dual pool model (Vt(scho)) (132.1 ml/g DM) and single pool model (Vt(orsk)) (131.5 ml/g DM) at 48 hours which was followed by that of Gliricidia sepium (116.1 and 113.5 ml/g/DM respectively) and Morus alba (116.9 and 113.7 g/kg DM respectively). At 48 hours, the Vt(scho) and Vt(orsk) for Trichanthera gigantea and Leucaena leucocephala were at the lower end of the range for the forages (Trichanthera gigantea: 70.8 and 65.7 ml/g DM and Leucaena leucocephala: 89.1 and 86.2 ml/g DM for the dual and single pool models respectively). Moringa oleifera was at the higher end of the range for the total volatile fatty acid (VFA) production whereas Trichanthera gigantea was at the lower end of the range. All MPTs except Trichanthera gigantea and Leucaena leucocephala, were more fermentable than the grasses and based on chemical composition, in vitro digestibility, fermentation parameters and end products, Moringa oleifera and Morus alba demonstrated overall high performance whereas Trichanthera gigantea performed poorly.