Effects of feeding quebracho tannin diets, with or without a dietary modifier, on rumen function in sheep

The effect of quebracho tannin (QT) on the activities of rumen microbes was studied both in vivo and in vitro. The in vivo study was carried out in fo ur rumen environments created by feeding four fistulated sheep a basal diet of chopped grass hay, grass cubes and whole barley (control) with or witho ut the addition of QT and the dietary modifier Browse Plus (BP). The active ingredients in BP are polyethylene glycol (PEG, more than 0.95 of the dry material), polyvinyl pyrrolidone (PVP) and calcium hydroxide. The diets off ered were control, control plus 50 g QT per kg diet (CQT), control plus 50 g QT per kg and 0.1 (CQT + 0.1) or 1.0 g BP per kg (CaT + 1.0). The experim ent was a 4 X 4 Latin-square design with periods of 4 weeks. Rumen liquor s amples were collected at 0, 2, and 8 h after feeding, 18 and 25 days after commencement of each period. Changes in flee and bound proanthocyanidin (PA ) concentrations, rumen pH, ammonia, volatile fatty acids (VFA), soluble pr otein concentrations, particle-bound cellulase and xylanase activities and rumen protozoal counts were used as indices of microbial activities. The sa me diets were incubated with rumen contents in vitro, except that the 0.1 g /kg level of BP was replaced by a fourth treatment made up of control plus 1.0 g BP per kg DM of hay (CBP). In vivo, bound PA concentrations in the ru men liquor of all the sheep given QT-containing diets were higher than thos e of the free PAs. The bound PA was higher (P < 0.05) in the rumen liquor o f sheep given CQT in comparison with those containing BP. There were reduct ions in ammonia (P > 0.05), soluble protein (P < 0.05) and total VFA (P > 0 .05) concentrations in the rumen liquor of sheep given CQT in comparison wi th those given the control and BP-containing diets. Reductions (P > 0.05) w ere also observed in the cellulase and xylanase activities of the rumen mic robes and in protozoal counts (P < 0.05) in the presence of ar in the diet. In vitro, QT reduced (P > 0.05) the viable bacterial counts, gas productio n and the total VFA concentrations after incubation. In both the in vivo an d in vitro experiments, BP was able to alleviate some but not all of the de pression in microbial activities. The main constituent (PEG) in BP binds to some of the tannins in solution and may displace tannins from tannin-prote in complexes.