| It is not conducive to exert the effect of conventional commercial lactic acid bacteria additives on improving silage quality due to inherently extreme and instable climate in Tibet.So it is important to discover and use suitable lactic acid bacteria to produce high quality silage in Tibetan.This study used crop straw silage as raw materials,screening and identification of low temperature-tolerant lactic acid bacteria strains that can express strong acid-producing and growth adaptability.On this basis,the effect of selected lactic acid bacteria strains on fermentation quality of grass and crop straw silages was evaluated in Tibet.That providing the oretical basis and technical support for the development and utilization of high quality low temperature-tolerant lactic acid bacteria additives in Tibet.1.The fermentation quality of crop straw silage in Tibet.The objective of this study was to evaluate the effects of glucose on the fermentation quality of crop straw silage prepared in Tibet.Silages were prepared with oat straw,corn straw,wheat straw and hullessbarley straw.The treatments as followed,the control(C),and 1%glucose(G).The silos were opened after 10 and 45 days of ensiling respectively,and then determined the fermentation quality.The results showed that it is easy to get high quality corn straw and oat straw silages with natural fermentation,however,the opposite results were found in barley and wheat straw silages.Adding glucose did not affect(P>0.05)the fermentation quality of crop straw silage.So the limiting factor of crop straw silage fermentation quality in Tibet is the insufficient quantity and activity of lactic acid bacteria.2.Screening,identification and physiological,biochemical properties of low temperature-tolerant lactic acid bacteria isolated from crop straw silage in Tibet.This experiment used hullessbarley straw,oat straw,wheat straw and corn straw silages of 10 and 45 days as research objects,and 20 low temperature-tolerant lactic acid bacteria strains were isolated from these silages and all the strains were homofermentative lactic acid bacteria,in which 8 strains were Lactococcus lactis and 12 strains were lactobacilli.Through acid-resistant experiment,all selected 20 lactic acid bacteria strains could grow well under pH value 3.5 to 7.0,particularly,strains of HG24,LH2,07,030,LOG5,LOG9,WG10,WG27,LW4,Ml,MG26,LMG4 could grow at pH 3.0,which indicated they had more acid resistance.All lactic acid bacteria strains showed salt resistance under 3%and 6.5%NaCl conditions.In the temperature experiment,all lactic acid bacteria strains could grow in the range of 5-30?.All the selected 20 strains can express strong growth adaptability under different conditions with pH values,salt and low temperature,in addition they could consume extensive carbon source,therefore,they might more suitable to adapt to extreme environment.Through morphous,physiological,biochemical characteristics and 16S rDNA sequence analysis,LH7,L07,L08,W34,LW7 and M3 5 were identified as Pediococcus.Pentosaceus,LH9 and LOG9 as Pediococcus.acidilactici,LM8 as Lactobacllus.coryniformis subsp.torquens and HG24,LH2,07,030,LOG5,WG10,WG27,LW4,M1,MG26 and LMG4 as Lactobacllus.Plantarum.As compared with the other three isolated lactic acid bacteria,Lactobacllus.Plantarum was more stronger in acid producing and growth rate.Among all strains of Lactobacllus.Plantarum strains,M1 showed the highest acid producing and growth rate;among all strains of Pediococcus.Pentosaceus,L07 showed the highest acid producing and growth rate;among all strains of Pediococcus acidilactici,LOG9 showed the highest acid production and the most rapid growth rate.Therefore,we selected strains of M1,LM8,L07 and LOG9 as silage additives and study the effects on fermentation quality of silage.3.The effects of low temperature-tolerant lactic acid bacteria on fermentation quality of Italian ryegrass silage at different temperaturesThe objective of this experiment was to evaluate the effects of low temperature-tolerant lactic acid bacteria on fermentation quality of Italian ryegrass silage at different temperatures.The treatments were as follow:the control(B)and four selected lactic acid bacteria treatments(Ml,LM8,L07,LOG9).All silos were opened after 30 days of ensiling,and then determined the fermentation quality.The results show that adding selected lactic acid bacteria improved the quality of Italian ryegrass silage at 25?,15 ?,10 ?,which was indicated by lower(P<0.05)AN/TN and acetic acid contents of the Italian ryegrass silages,and higher(P<0.05)LA/AA,lactic acid,and WSC contents.M1 silage was the best at 25?,while LM8 silage was the best at 10? and15?.In conclusion,the result in this experiment showed that Lactobacillus LM8 was more suitable for using as silage additive at low temperatures.4.The effects of low temperature-tolerant lactic acid bacteria on fermentation quality of tall fescue and oat straw silages in Tibet.The objective of this experiment was to evaluate the effects of low temperature-tolerant lactic acid bacteria on fermentation quality of tall fescue and oat straw silages.The treatments were as follow:the control(B),commercial lactic acid bacteria treatment(G)and four selected lactic acid bacteria treatments(M1,LM8,L07,LOG9).All silos were opened after 40 days of ensiling,and then determined the fermentation quality.The results showed that the four selected lactic acid bacteria treatments improved the fermentation quality of tall fescue and oat straw silages,Adding selected lactic acid bacteria significantly(P<0.05)reduced the pH value,AN/TN and acetic acid contents of tall fescue and oat straw silages and significantly(P<0.05)increased the LA/AA,lactic acid,and WSC contents.The result in this experiment showed that M1 was the most suitable for application in tall fescue silage,and LOG9 was the the most suitable for application in oat straw silage. |
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