RUMEN DEGRADABILITY AND INTESTINAL DIGESTIBILITY OF BREWERS GRAINS ASAFFECTED BY ORIGIN AND HEAT-TREATMENT AND OF BARLEY ROOTLETS

The rumen degradability and intestinal digestibility of dry matter (DM ) and nitrogen (N) of three samples of brewers' grains (BG) and three of barley rootlets (BR) were determined. Rumen degradability was deter mined by the nylon bag technique in three rumen fistulated wethers. In testinal digestibility was determined by the mobile nylon bag techniqu e in two duodenal fistulated wethers. N content ranged from 41.2 to 46 .4 g/kg DM for BG, and from 42.8 to 53.7 g/kg DM for BR. N effective d egradability (NED), calculated for rumen outflow rates determined in e ach sheep, ranged from 57.2% to 70.9% for BG and from 79.0% to 84.0% f or BR. N intestinal digestibility (NID) determined on 8 h-rumen incuba ted residues, ranged from 84.9% to 89.8% for BG and from 67.3% to 81.3 % for BR. Lower rumen degradability was partially compensated by highe r intestinal digestibility, resulting in a smaller variation in the es timated amount of digestible bypass N, which ranged from 24.7% to 36.7 % for BG and from 10.8% to 17.1% for BR. One BG sample was selected to study the effects of heat treatment (HT) on its chemical composition, rumen degradability and intestinal digestibility. The BG sample was e ither freeze-dried (UBG) or dried at 50 degrees C (50BG), 100 degrees C (100BG), 135 degrees C (135BG) and 175 degrees C (175BG). Total N co ntent was not affected by HT, but the acid-detergent insoluble N (expr essed as percentage of total N content) increased from 13.7% to 54.1%. HT reduced the NED (from 76.5% to 25.6%) and, as a consequence, the s upply of undegraded N to the duodenum was increased by 1.2, 1.8, 2.4 a nd 3.2 times for 50BG, 100BG, 135BG and 175BG, respectively. Drying at 50 degrees C and 100 degrees C had no adverse effects on the NID dete rmined on 8 h-rumen incubation residues (mean value of 84.3%), but dry ing at 135 and 175 degrees C decreased it to values of 80.1 and 51.6%, respectively. As a consequence, the estimated amount of digestible by pass N was increased by 1.2, 1.8, 2.3 and 1.9 times when drying at 50 degrees C, 100 degrees C, 135 degrees C and 175 degrees C, respectivel y. (C) 1998 Elsevier Science B.V.