Quebracho tannins with or without Browse Plus (a commercial preparation of polyethylene glycol) in sheep diets: effect on digestibility of nutrients in vivo and degradation of grass hay in sacco and in vitro

Quebracho tannins (QT, 50 g/kg diet), with or without two levels (0.1 or 1.0 g/kg diet) of a commercial additive containing polyethylene glycol (Browse Plus), were fed to four cannulated sheep receiving a basal diet of grass hay, grass cubes and whole barley at maintenance level in a 4 x 4 Latin square over periods of 4 weeks. The control treatment consisted of the basal diet alone. Ruminal in-sacco degradation and in-vitro gas production were measured. Apparent digestibilities of all nutrients were significantly (P < 0.05) depressed by the QTs. Browse Plus was able to remove some, but not all, of the depressions in digestibilities, with the higher level of Browse Plus (1 g/kg diet) tending to produce a significant (P < 0.05) improvement in the digestibilities of all nutrients. The lower level of Browse Plus used (0.1 g/kg) slightly (P > 0.05) improved the digestibilities of all nutrients. There were no differences (P > 0.05) in the degradation and rate of degradation of the hay incubated in sacco in the four rumen environments created by the different tannin content of the experimental diets. However, the rate of degradation of the insoluble but potentially degradable fraction was lowered by the QT diet, indicating the possibility of reduced microbial cellulolysis. Microbial activities measured from gas production were also reduced in vitro. However, unlike the in-vivo and in-sacco experiments, Browse Plus in vitro removed all the depressions in activities of the microbes that could be associated with the tannins. Although Browse Plus was unable to alleviate all of the depression in digestibilities in vivo, it may still be a useful digestive modifier which partly offsets the inhibitory effects of condensed tannins in ruminant diets, especially in arid environments with poor quality feeds. (C) 1997 Elsevier Science B.V.