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Castrated male sheep were fed with 5 different rations varying in the straw to concentrate ratio between 100: 0, 75: 25, 50: 50, 25: 75 and 0: 100. Ground barley, ground corn and dried sugar beet pulp were used as concentrate sources. Chopped winter wheat straw was fed as roughage source. All rations were supplemented with a protein-mineral-vitamin-premix. In sacco dry matter degradability of artificially dried ryegrass, untreated and ammonia treated wheat straw was measured within three rumen fistulated sheep. Nylon bags were incubated for 48 h in the rumen of sheep. Volatile fatty acids of rumen fluid were determined by gas chromatography. Samples were taken via rumen fistula 3 h after morning feeding. Apparent digestibility of organic matter and fibre fractions of total rations were determined within five sheep. Increased concentrate portion decreased in sacco dry matter degradability of incubated roughages. Decrease of dry matter degradability was much higher for ammonia treated (from 55.0 to 22.5%) and untreated straw (from 50.9 to 22.7%) than for ryegrass (from 75.6 to 69.2%), when concentrate increased from 0 to 100% of ration. The highest concentrate portions did not show any increase of degradability of ammonia treated straw. Specific concentrate effects were observed when 75 and 100% concentrate were fed (unphysiological level). Ground barley as concentrate source decreased rumen pH to a larger extent (down to 5.18) than corn and sugar beet pulp (down to 5.60 and 5.57). Sheep suffered from rumen acidosis in some cases. Higher concentrate levels increased concentration of total volatile fatty acids of rumen liquid and molar concentration of propionate and butyrate, but decreased acetate. Various concentrate sources showed different influences on parameters of rumen fermentation. Apparent digestibility of organic matter of total rations increased from 52.7 to 86.1% if concentrate portions enhanced from 0 to 100%. High portions of ground barley decreased cellulolytic activity and fibre digestion. On the other hand high levels of sugar beet pulp increased digestibility of crude fibre and neutral detergent fibre.

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Two series of experiments with rumen fistulated castrated male sheep and goats were carried out. In experiment I three sheep each consumed rations rich in concentrate (700 g concentrate, 200 g chopped wheat straw) or roughage (700 g artificially dried ryegrass, 200 g chopped wheat straw per animal per day) and supplemented with 0, 1, 2 or 4 g Yea-Sacc (Saccharomyces cerevisiae; USA) per sheep per day. In experiment II three sheep were fed with 1000 g artificially dried ryegrass and 200 g concentrate, three goats consumed 750 g ryegrass and 150 g concentrate. 0, 0.5, 1 or 2 g Levaferm (Saccharomyces cerevisiae; Germany) per animal per day were added. Rations of all animals were supplemented with minerals and vitamins. After 14 days of feeding wheat straw, ammonia treated wheat straw and artificially dried grass (exp. I) or wheat straw and artificially dried grass (exp. II) were incubated in nylon bags in the rumen for 6, 12, 24, 48 and 72 hours. At the end of the experiments rumen fluid was taken via cannulae and parameters of rumen fermentation were measured. Higher levels of added Yea-Sacc decreased in sacco dry matter degradability of all incubated feeds. Depression was much higher if Yea-Sacc was added to the concentrate ration (overall mean for 24, 48 and 72 h incubation time: 55.1, 47.1, 46.1 and 44.5 for 0, 1, 2 and 4 g Yea-Sacc) than to the roughage diet (58.7, 56.3, 55.0 and 54.1%). Levaferm did not significantly influence the rumen dry matter degradability of incubated feeds (overall mean for 24, 48, and 72 h incubation time: 64.0; 64.9; 64.9 and 64.2% for sheep; 63.0; 63.2; 63.2 and 61.6% for goats, if added with 0, 0.5, 1 and 2 g Levaferm per animal per day). Rumen pH, concentration of volatile fatty acids and molar concentration of fatty acids in rumen fluid were not significantly influenced by added yeasts. More research seems necessary to find out the mode of action of yeast and to quantify and to reproduce the effects of added yeast.

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