| Six experiments were conducted to investigate the factors influencing qualitative parameters of urea-molasses-mineral blocks (UMMB) and the effects of yeast culture (YC) or / and cellulolytic enzymes (CE) included in UMMB on manipulation of ruminal fermentation, improvements in ruminal fiber degradation and in growth performance of steers.The purposes of Exp.l and Exp.2 were to investigate the effect of the proportion of major components and binding materials on the qualitative parameters of the blocks and their daily consumption by growing steers. With increasing pressure, the hardness and density of the block were increased (Quadratic; P<0.001), but expansibility of diameter and thickness and daily consumption of the blocks significantly decreased (Quadratic; P<0.001), suggesting having an appropriate pressure at20 Mpa. The hardness, density and expansibility of UMMB were significantly influenced bypost-solidification time (P<0.001). Increasing the level of addition of molasses and CaO resulted in anevident increase in the hardness and density of UMMB (P<0.05). Nine types of urea- molasses-mineral block licks were stored for 15 day under higher temperature (36~40℃) and higher relative humidity (80~90%) conditions, the hardness and consistency of blocks significantly increased (P<0.05), but expansibility of diameter and thickness of blocks significantly decreased (P<0.05) with increasing urea and common salt levels, respectively. It is concluded for this experiment that the acceptable quality parameters of the UMMB would be achieved by supplementation of molasses, CaO, MgO, andbentonite at the level of 12%, 5%, 2~4%, and 5~10%, respectively.Exp. 3 and Exp.4 were conducted in vitro to study the effect of YC or CE included in UMMB on rumen fermentation and fiber degradation characteristics, and the ability of cellulose adhesion by mixed ruminal bacteria isolated from animals feeding YC or CE blocks included in UMMB. The ruminal gas production and both dry matter and cell wall degradation rates were significantly enhanced by the supplementation of UMMB (P<0.01), of which the greatest gas production and the degradation rates were found with YCB treatment, followed by YCCEB and CEB treatments with treatment B having the lowest values. The addition of blocks led to a decrease in pH values, but an increase in the concentration of total volatile fatty acids and NH3-N of in vitro ruminal fluid, which indicated that YC functions best for manipulating ruminal fiber fermentation. The total bacterial counts, CMCase, xylanaseactivities and adhesion ability to crystalline cellulose were all increased significantly (P<0.05 or P<0.01) due to supplementation of YCB and YCCEB, but there were no significantly difference in crystalase activity (P>0.05) between the treatments.Certain components of YC or CE included in UMMB probable have a selective role for ruminal cellulolytic bacteria, which would enhance the extent of adhesion to crystalline cellulose and corresponding degradation.The effect of inclution of YC or CE in UMMB on rumen kinetic degradation and and total tract digestibility was studed in Exp 5 using four rumen cannulated Holstein steers in sacco. When blocks containing B, YCB and CEB were fed, the degradation rates of NDF were 0.041/h, 0.050/h, and 0.043/h,and of ADF were 0.037/h, 0.042/h, and 0.050/h, compared with the control of 0.032/h for NDF and 0.028/h for ADF, respectively (p <0.05). AS different UMMB was fed to the rumen, the fraction of slowly and fast degradable ADF (P<0.00), the effective degradability of NDF and ADF (p <0.05) were increased significantly, as compared with the control treatment. When the YC-containing blocks were added in the rumen, there was a significant difference in apparent CP digestibility of total tract (p <0.05), but there was no difference in the digestibility of DM, NDF and ADF relative to B (P>0.05). The total tract digestibilities of DM, NDF and ADF significantly increased due to ruminai addition of CEB (P<0.05). This experiment indicates that rumi...
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