Effect of saliva from sheep that have ingested quebracho tannins on the in vitro rumen fermentation activity to digest tannin-containing shrubs

This work was designed to assess the nutritional influence of pre-incubation in saliva on in vitro fermentative activity when some tanniniferous shrubs were incubated in batch cultures of mixed ruminal microorganisms. Saliva was collected from eight Merino sheep allocated in two experimental groups, namely control (SC) and quebracho (SQ) groups fed one kg alfalfa hay daily. Sheep of SQ group were given daily alfalfa hay supplemented with 50 g quebracho/kg dry matter for 60 days, whereas sheep of SC group were always given unsupplemented alfalfa hay. Foliage of six shrub species (Cytisus scoparius (Scotch broom), Genista florida (Iberian silver-leaved broom), Rosa canina (wild dog rose), Quercus pyrenaica (hoary oak), Cistus laurifolius (laurel-leaved rock-rose) and Erica australis (Spanish heath)) was collected from uplands in the province of León (Norwest Spain) in spring and in summer/autumn and used in the study. Samples were pre-incubated in each saliva source for 4 h at 39 °C, followed by an incubation in buffered rumen fluid to determine their in vitro dry matter digestibility (IVD) and gas production kinetics. For all treatments, rumen fluid was obtained from sheep of control group. Regardless the large differences among the plant browse species used in the study in their tannin contents, IVD and rate and extent of degradation (based on gas production parameters), there were no significant differences between SC and SQ saliva in any of the variables studied. Accordingly, it was suggested that sheep supplemented with quebracho tannins did not produce salivary proteins to protect against negative effects of tannins on digestion of plant material, and that the feedback mechanism may not have evolved or may have become lost. Further studies on the effect of tannins on saliva chemical composition in sheep would be timely.