| With the development of animal husbandry, and feed resources is short, China has abundant resources of crude feed, but we can not be used effectivly because livestock and poultry have a poor digestion and absorption of crude feed, how can we effectively use of crude feed resources is a concern to contemporary researchers and producers. Second only to cellulose in natural abundance,xylan is a major component of hemicellulose fraction of the plant cell walls. The xylan existing in grain feed is a major kind of anti-nutritional factors,it can reduce feed digestibility significantly and hinder the growth of livestock and poultry. Xylanase can degrade xylan into oligosaccharide or xylose,which can be absorbed by animals.The method that xylanase degradation of xylan to eliminate anti-nutritional is safe and effective.The aim of this experiment is to screen a high-xylanase producing bacterium from rot corn stalks,through transparent ring, reaserch the optimization of xylanase production conditions and characterization of xylanase and investigate effect of different levels of xylanase(0,500,1000,1500U/kg) on growth Performance and nutrient utilization. This test was described in the following three sections.(1)Screening of xylanase producing strain. Xylanase can degrade xylan into oligosaccharide or xylose ,which can not be stained by congo red so we can see transparent ring , according to the size of the transparent circle,select a high-produced strain. The gathered samples,at first,are dealed with the processing of spored is posing process,then through the first sceening and the second sceening on the filtrate culutre medium,at last acquire a high-xylanase producing bacterium,naming SX5-3. Under the strain of Gram staining, morpHological characteristics and 16SrDNA identification, to determine the strain is Bacillus pumilus.(2)Study of production conditions and characterias. The optimized conditions were established by single factor test .The results showed that the bacteria had the logarihtm growth period at 12h and reached the peak of growth at 36h. Optimum temperature was 37℃, pH was 6.5-7.5.Inorder to supply the effiency nutrition for the bacterium,carbon and nitrogen sources were optimized. Single factor test using five different carbon sources and four different nitrogen sources respectively,is cultured under suitable conditions. The results showed that: the xylan as carbon source, yeast extract as nitrogen source, bacteria grew well and showed high activity.Changing the temperature and pH value, to determine the SX5-3 bacteria optimum reaction conditions.The results showed that the enzyme had the highest enzyme activity in the temperature of 55℃, pH 6.0. When the temperature is 60℃, the remain of enzyme activity is 80%, it is proved this xylanase is midtempreutre-resistant. when the pH was 7, the remain of enzyme activity is 85% of the highest enzyme activity, pH 5.5, 65% of the enzyme activity was remained, indicating that the enzyme neutropHil acidic.(3)Effect of the xylanase on broilers performance and nutrient utilization. One hundred and eighty one-day-old AA broilers were randomly divided into 6 treatments with 6 eplicates of 5 chickens,to investigate effect of different levels of test xylanase(0 , 500 ,1000,1500,2000U/kg) and commodities enzyme (1000U/kg)on growth Performance and nutrient utilization. The results showed that:Compared with the control, groups feed with 1 000 U/kg xylanase significantly increased 22 ~ 42d and1 ~ 42 broiler weight gain (P <0.05), and reduced the 1 ~ 21d , 22 ~ 42d and 1 ~ 42 broiler feed intake and feed conversion ratio (P <0.05); Energy, crude protein and crude fiber utilization is increased by 2.35%, 4.79%, 3.18% for 1 ~ 21d and 1.71%, 4.91%, 2.87% for 22 ~ 42d ( P <0.05), respectively. Compared with the commodities enzyme, daily gain, feed intake, feed conversion ratio and the nutrient utilization were not significantly different (P> 0.05)... |
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