| A study on the dynamic changes of the on populations of three species of cellulolytic bacteria in the rumen of sheep fed dietary with different quality of forage using oligonucleotide probes to rRNA and traditional cultivation methods was carried out. The mechanism of the rumen microorganism how to degrade the fiber , through exploring the relationship among rumen microflora,rumen fermentation and degradation of dietary fiber was elaborated. Under adding or not adding yeast culture condition, nine Inner Mongolian wether sheep with ruminal cannula, healthy , weighting 45Kg, were randomly divided into three groups fed three diets with different dietary forage quality on the same dietary ratio of forage to concentrate(R/C)of 8:2, higher forage grading group (H group had GI value of 2.89MJ),middle one (M group had GI value of 1.73 MJ),low one(L group had GI value 0.65 MJ) according to Grading Index(GI) of forage .This experiment included two stages, and experiment animals were added yeast culture in the second stage. The results of this study were as follows1. The total bacteria counting and the populations of B.succinogenes in the rumen were affected significantly by different dietary forage quality (p<0.05). The total bacteria counting increased gradually(p<0.05) and the population of B.succinogenes had an ascendant tendency when GI increased. No significant difference was found in the populations of R.flavefaciens and R.albus by different dietary forage quality(P>0.05). The difference of the total cellulolytic bacteria counting among three groups were not significant (P>0.05), the total cellulolytic bacteria counting increased gradually when GI increased. The populations of R.flavefaciens increased significantly(p<0.05) ,and the total population of rumen bacteria and cellulolytic bacteria counting in the rumen tended to increase after yeast culture supplemented.2. The mean value of relative populations of R.flavefaciens,R.albus and B.succinogenes in the rumen bacteria were 1.18%,2.44% and 10.07%, respectively, and the total cellulolytic bacterial counting was 13.68%. Three species of ruminal cellulolytic bacteria counting and rumen bacteria could reach peak value at 4-8h after feeding.3. The ruminal pH,ORP,concentration of BCP(p>0.05) were not affected significantly by different dietary forage quality. When GI increased, the ruminal pH and concentration of BCP tended to increase; ORP has a descendent tendency(p>0.05); ruminal NH3-N concentration increased gradually, and H group was higher than L group(p<0.05); the concentration of acetic acid tend to increase; at the same time the concentration of propanoic acid displayed an ascendant tendency; the ratio of acetate to propionate was lower. The difference of mean values of TVFA concentration among three groups weren't significant(p>0.05).4. The ruminal pH tend to reduce, the concentration of NH3-N and BCP tend to increase(p>0.05). The concentration of acetic acid was increased very significantly(p<0.01), the concentration of individual VFA and TVFA were increased, and the ratio of acetate to propionate was increased after feeding yeast culture.5. The quantitis of Entodinium and total protozoa in the rumen were affected significantly by different dietary forage quality, H group was higher than L group (p<0.05), No significant difference was found in the populations of Diplodinium,Ophryoscolex,Epidinium and Isotricha among the four groups. The total protozoa counting was increased after yeast culture added(p>0.05), especially the Entodinium and Diplodinium counting.6. The ruminal effective degradability of dry matter and ADF were not influenced by different dietary forage quality(P>0.05), but NDF ruminal effective degradability was affected significantly,and H group was higher than L group(P<0.05). The ruminal effective degradability of DM and NDF tended to increase after feeding yeast culture to sheep. The xylanase activity in every group increased gradually and H group was higher than L group when GI increased(P<0.05). The activity of FPA and pectinase were not affected significantly by different dietary forage quality(P>0.05), the activity of xylanase,FPA and pectinase were higher before feeding, and all values reached the peak value at 8h-12h after feeding. The activity of xylanase and pectinase tended to increase after yeast culture supplemented.
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