In vitro ruminal fermentation of Pennisetum purpureum CT-115 supplemented with four tropical browse legume species

An in vitro gas production experiment was completed to determine effects of four tropical browse legumes (i.e., Acacia cornigera, AC; Albizia lebbekoides, AL; Enterolobium cyclocarpum, EC; Leucaena leucocephala, LL) at 0.15 or 0.30 of total substrate on microbial fermentation of the tropical grass Pennisetum purpureum CT-115 (PP). Two incubation runs with four bottles per treatment were completed, using two bottles for gas production measurements up to 96 h and two bottles for microbial purine bases (PB) concentration analysis after 24 h. Inclusion of AC, EC and LL linearly increased (P<0.05) gas production from PP alone at an initial stage of fermentation (5 h) because of their higher fermentation rate versus PP. However, whereas the linear increase in gas production was maintained at mid fermentation (i.e., 24 h) with AC, there was no effect with LL and a linear reduction in gas volume at 24 and 96 h with EC, possibly because of its saponin content. Gas production with AL was linearly reduced at 24 and 96 h (P<0.01). There were no differences in microbial concentrations, either estimated from a partitioning factor or PB analysis, but PB concentration in the solid residue increased three-fold when LL were included. Differences among legume species in chemical composition, and in the nature of their secondary compounds, are responsible for the fermentation pattern of mixed substrates.