Microbial colonization and degradation of forage samples incubated in vitro at different initial pH

Microbial colonization, degradation, and gas production kinetics of tropical and temperate forage samples incubated in vitro at initial pH (pHi) of 5.5, 6.0, 6.5 and 7.0 were measured. Dried, ground samples of oat (Avena strigosa), ryegrass (Lolium multifllorum), dwarf elephant grass (Pennisetum purpureum Schum. cv. Mott.) and ricegrass (Echinochloa sp.) were used. Microbial colonization on residues and extent of degradation were higher for temperate than for tropical forage samples (P<0.05). Initial pH did not affect microbial colonization on residue, but the extent of in vitro degradation was directly related to pHi for both forage types (P<0.05). Kinetics of fermentation of temperate and tropical forage samples, however, reacted differently to both the incubation method (i.e., in vitro or in vitro/gas) and the pHi.