Italic textAbstract. Industrial Streptomyces avermitilis were irradiated by 80 MeV/u 12C6+ ions whith were provided by the Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou Heavy Ion Accelerator. The high titers of mutants were obtained with different doses. The original strains and the high titers of mutants were detected and analyzed by Random Amplified Polymorphic DNA technology (RAPD). The results show that bands could be got from amplify the original strain by 4 primers of 28 primers and the high titers of mutants were amplified by the 4 primers. The amplified products were analysed by Jaccard formula. After 10 Gy, 30 Gy, 40 Gy, 45 Gy, 50 Gy, 70 Gy isodose irradiation, the similarity index were 0.63, 0.75, 0.71, 0.8, 0.61, 0.73. It was confirmed that at the DNA level, not only the high titers strains and the original mutant strain’s DNA were different, but also the high titers of the different mutants’ DNA were different. Therefore, ion implantation method changed the different Streptomyces avermitilis genetic material which promote the importance trace of avermectin biosynthesis changed, and different high titers of Streptomyces avermitilis were obtained.

Heavy ion irradiation induced mutation is a unique method of physical mutation, with various parameters, high LET and RBE characteristic. The spore suspension of streptomyces avermitilis were irradiated by carbon ions with doses of 0、30、40、50、60 and 70 Gy. The high avermectin producing strain was successfully obtained after the mutagenesis processing by heavy ion beam and the screening of orthomutation strains. Two strains(No.203 and No.148) which potency was 5200μg/ml was sieved and its potency increased 38.64% than the original strain. The obtained strains were used for 1 ton fermentation tank and the pilot 5-ton fermentation tank amplification tests.

The objective of this study was to research the influence of the sweet sorghum straw fermented by the Compound Microbial Agent on the milk yield and milk composition of the cows. The results indicated that sweet sorghum straw bio-feed fermented by the Compound Microbial Agent in bags could increase the feed intake (11.4%) and milk yield(14.2%) compared with the control group, it also has improved milk protein (14.03%) and butterfat rate (16.3%) ,and has reduced the somatic cell's number(5.15%) compared with the control group. The sweet sorghum straw fermented by the Compound Microbial Agent has reduced the milk-feed ratio (20.8%).It has improved the feed digestibility and utilization and reduced the costing.

The results indicated that the sweet sorghum straw bio-feed fermented in bags and cellar pits by the Compound Microbial Agent both could increase the content of the crude protein (CP) and reduce the content of the fibrinogen (FIB) compared with control group. The content of CP in bags fermented by Complex Microbial group has increased 71% and the content of FIB has reduced 8%. The CP content of cellar pits fermented by Complex Microbial group has increased 91% and the FIB content has reduced 24.5% . Compared with Silage corn stalks group , sweet sorghum straw bio-feed fermented by the Compound Microbial Agent could also improve the content of milk protein (14.03%,16.81%) and butterfat rate (16.3%, 92.98%) and reduce the somatic cell's number (5.15%,6.86%) in the milk. It has promoted the cows capacity to produce milk and also improved the quality and flavor of dairy product.