Influence of the ratio between wheat straw and ground barley, ground corn or dried sugar beet pulp on in sacco dry matter degradation of ryegrass and wheat straw, rumen fermentation and apparent digestibility in sheep.

Abstract

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.