| Due to higher protein content and buffer,it is is difficult for Alfalfa to make silage successfully.Sweet sorghum belongs to C4 plant with high content of sugar,high photosynthetic efficiency,high biological yield,drought and salt tolerance,and strong resistance,and can be made silage easily.In theory,mixed silages made by sweet sorghum and alfalfa can overcome its' defects and improve the balance of energy and protein in diet.Therefore,in this experiment,different proportions of sweet sorghum and alfalfa(0:100,0%SS;20:80,20%SS;40:60,40%SS,60:40,60%SS;80:20,80%SS;100:0,100%SS)were designed to make mixed silages,and the relationships were investigated between mixed proportions and silage quality,nutritional characteristics,mirobe change and aerobic stability by sensory evaluation,and the analysis of nutrients,fermentation,bacterial diversity and aerobic stability.The purpose of this study is to provide experimental data for the scientific utilization of sweet.The results of sensory evaluation,nutrients and fermentation analysis of different proportions of mixed silages showed that 40%SS mixed silage had the best silage quality with higher rate of success silage,intactive structure,good smell,and protein content.18 strains of Lactic acid bacteria(LAB),4 strains of Lactobacillus rhamnosus,5 strains of Lactobacillus plantarum,3 strains of Enterococcus,2 strains of Leuconostoc mesenteroides subsp,2 strains of Enterococcus faecium,1 strain of Lactococcus lactis and Lactobacillus respectively isolated from the mixed silages,and Lactobacillus plantarum had high ability of acid production and fast growth rate.The results of study of mixed silages with different proportion of sweet sorghum and alfalfa on silage pH,organic acids and main microbial number showed that pH had fastest decrease in 100%SS mixed silage,and reached the lowest pH after 45 d of ensiling.The number of LAB and the content of Lactic acid and acetic acid increased with the prolong of fermentation time,and the content of Lactic acid,acetic acid and number of LAB in 100%SS mixed silage were significantly higher than other proportions.The number of yeasts,molds and aerobic bacteria decreased with the extension of fermentation time,among them,the yeasts and molds in mixed silage of 80%SS and 100%SS respectively were disappeared at 25 d and 10 d.The results of PCR-DGGE analysis of LAB diversity in mixed silages shown that the kinds of LAB community decreased with the increase of the proportion of sweet sorghum in mixed silage,and 20%SS,40%SS and 60%SS proportions had the much more types of LAB,while the least in 100%SS mixed silage.The domiant LAB in mixed silage with 0%SS,20%SS,40%SS,60%SS,80%SS were Lactobacillus rhamnose and Enterococcus faecium,but L.mesenteroides subsp.mesenteroides and Enterococcus faecium were dominant LAB in 100%SS.The similarity of LAB between 100%SS and other mixed silages was only 32%.However,the compositions of LAB community in 0%SS and 20%SS,40%SS and 60%SS were almost the same.Community similarity of LAB among 0%SS?20%SS?80%SS and 60% SS was 70%.Study on the aerobic stability and microbial number of the mixed silage showed that aerobic stability decreased with the increase proportion of sweet sorghum in the mixed silages,and alfalfa silage had the best aerobic stability.The number of LAB decreased while yeast,mold,aerobic bacteria and pH increased gradually with increase of the exposure time.At the same time of aerobic exposure,the number of yeast and aerobic bacteria increased while mold decreased significantly with increase of proportion of sweet sorghum in the mixed silage.All in all,adding small amount of sweet sorghum can obviously increase the success rate of silage,and also adding a certain of sweet sorghum to the mixed silage is beneficial for improving the aerobic stability and inhibiting the growth of mold. |
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