Leaves from 4 shrub species (Erica australis, Cistus laurifolius, Quercus pyrenaica, and Rosa canina) collected from the mountain of Leon (northwestern Spain) were used to test the medium-term effects of the intake of quebracho condensed tannins on the fermentative activity in the rumen of sheep. Leaves from all shrubs were sampled at 3 different maturity stages (spring, summer and autumn). Eight Merino rumen cannulated sheep fed chopped alfalfa hay were used. Four sheep were given alfalfa hay treated with 50 g quebracho/kg DM for 60 d (group Q), whereas the other animals were always given untreated alfalfa hay and used as the control group (C). Differences in the fermentative activity were examined in vitro in batch cultures inoculated with rumen fluid obtained on d 60 from both groups of sheep. In vitro dry matter digestibility (IVD) and gas production kinetics from leaves and flowers of all shrub species were determined. Except for the flowers of C. laurifolius, IVD was higher (P < 0.05) when rumen fluid from Q sheep was used. Likewise, a significant effect of inoculum source on the dry matter disappearance after 144 h of incubation was observed for the flowers of E. australis. For the same substrate, the inoculation with rumen fluid from Q sheep resulted in a higher gas production at 24 h and faster fractional gas production rates. The differences were generally statistically significant (P < 0.05) in most comparisons and the magnitude of this effect was greater when material with higher tannin contents was incubated (leaves of E. australis and C. laurifolius). In conclusion, rumen fluid from sheep fed a diet supplemented with condensed tannins showed a higher fermentative activity to degrade tannin-rich browse. This could be due to the appearance and proliferation of tannin-tolerant bacterial species or to the induction of changes in the existing bacteria to enhance their tolerance to these phenolic compounds.

1 Página.--Trabajo presentado al 2010 Annual Meeting Abstracts (Denver, Colorado, 11 al 15 de Julio del 2010).--J. Anim. Sci. Vol. 88, E-Suppl. 2/J. Dairy Sci. Vol. 93, E-Suppl. 1/Poult. Sci. Vol. 89, E-Suppl. 1

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