Chemical composition and relationship to in vitro gas production of Zimbabwean browsable indigenous tree species

Seventeen Zimbabwean browse species were analysed for crude protein (CP), neutral and acid detergent fibre (NDF and ADF), acid detergent lignin (ADL), insoluble proanthocyanidins (IPAs) and protein precipitating polyphenolics (PPPs). Gas production of the species was measured over 96 h and gas-production constants estimated using the equation: gas produced = b(1 − e−ct). The browse varied greatly in their CP, fibre and phenolic content. Crude protein ranged from 56 to 210 g kg−1 dry matter (DM), NDF from 294 to 835 g kg−1 DM and PAs from 14.2 to 389 A550 nm g−1 NDF. None of the polyphenolics assayed were related to gas-production constants (P > 0.05) but NDF, ADF and ADL were negatively correlated (P < 0.05) to rate and extent of gas production. The results indicate that the effect of polyphenolics on gas production is complex and varies across browse species and that the fibre fraction of browse may be more important than tannins in limiting fermentation in vitro.