The effectiveness of adapted rumen fluid versus PEG to ferment tannin-containing substrates in vitro

This study investigated the potential of the goat's ruminal adaptation to reduce the negative effect of tannins on in vitro fermentation. Rumen fluid was obtained from goats fed a mixture of tannin-containing tree fruits (adapted rumen fluid) or tannin-free commercial protein supplements (unadapted rumen fluid) for 85 days. Dry, mature fruits of Acacia nilotica, Acacia erubescens, Acacia erioloba, Dichrostachys cinerea and Piliostigma thonningii were used as substrates for the in vitro fermentation. The effectiveness of adapted rumen fluid to ferment tannin-containing substrates was compared to the extent of fermentation when tannins were inactivated with polyethylene glycol (PEG), a known tannin-binding agent. Adapted rumen fluid (P<0.05) increased gas production from all five substrates between 15.8% and 73.7%. In A. nilotica, D. cinerea and P. thonningii, this increase was less than that obtained through PEG treatment. When PEG was added to adapted rumen fluid a further improvement in extent of fermentation was observed in four out of the five fruit samples. The largest PEG effect when incubated with adapted rumen fluid was observed in A. nilotica (43.1%) and D. cinerea (42.9%) fruits. It is concluded that some tannin-rich feedstuffs may still benefit from treatment even when these are offered to adapted animals.