Feeding quebracho tannins to sheep enhances rumen fermentative activity to degrade browse shrubs

Twenty-four samples of leaves, flowers and fruits of five browse plant species (i.e., Erica australis; Cistus laurifolius; Quercus pyrenaica; Cytisus scoparius and Rosa canina) collected from spring to autumn at uplands in the province of Leَn (NW Spain) were used to explore medium-term effects of intake of quebracho condensed tannins on fermentative activity in the rumen of sheep. The objective was to determine if adaptation to tannins at the rumen level may develop in response to regular consumption of tannins, resulting in an enhanced ability to digest browse forages. Eight rumen cannulated Merino sheep fed chopped alfalfa hay were used. Four sheep were fed alfalfa hay supplemented with 50 g quebracho/kg dry matter (DM) for 60 days and used as the treated group (QT sheep), whereas the other sheep were always fed untreated alfalfa hay and used as the control group. Differences in the fermentative activity were examined in vitro (DM digestibility (IVD) and gas production kinetics) in batch cultures inoculated with rumen fluid obtained on day 60 from both groups of sheep. With most browse samples, incubation in rumen fluid from QT sheep resulted in higher IVD, gas production at 24 h, fractional gas production rate and extent of degradation in the rumen compared with incubations in rumen fluid from control sheep. The magnitude of this effect was greater when browse with higher tannin content was incubated (leaves of E. australis and C. laurifolius). Rumen fluid from sheep fed a diet supplemented with condensed tannins had enhanced fermentative activity to degrade tannin-rich browse, which could be due to the appearance and proliferation of tannin-tolerant bacterial species and/or to stimulation of changes in the existing bacteria to enhance their tolerance to these phenolic compounds.