Effects Of Bacteria-Enzyme Combination On Quality,Microbial Community Structure And In Vitro Rumen Fermentation Characteristies Of Sweet Sorghum With Different Stubble Height

Sweet Sorghum(Sorghum bicolor L.),as a C4 crop,contains a lot of carbohydrates and a small amount of crude protein and crude fat in the above-ground part,which is a silage crop with great development potential.However,the high cellulose content and low dry matter digestibility of sweet sorghum severely limit its promotion and application as high-quality feed.Therefore,in this experiment,sweet sorghum was used as silage material,and a 4 × 4 random block design was adopted to study different stubble heights(L,15 cm;ML,25 cm;MH,35 cm;H,45 cm)treated with different additives(In control group CON,only distilled water was added,BC was treated with Bacillus coagulans,the addition amount was 106 CFU/g fresh weight;CE was treated with cellulase and added at 0.2 g/kg fresh weight.BE was enzyme combination treatment,with Bacillus coagulans 106 CFU/g fresh weight+cellulase 0.2 g/kg fresh weight)on sweet sorghum silage quality,microbial community structure and in vitro fermentation characteristics.This provides a theoretical basis for the development and utilization of sweet sorghum green silage quality and coarse feed resources.The main research results are as follows:(1)With the increase of stubble height,the water soluble carbohydrates(WSC)content of sweet sorghum silage,crude protein(CP),lactic acid(LA),and acetic acid(AA)showed an upward trend,while the content of neutral detergent fiber(NDF),acid detergent fiber(ADF),NH3-N,and pH showed a downward trend.However,there was no significant difference between the MH and H stubble height(P>0.05).Compared with the CON group,the CE treatment group significantly reduced the NDF(4.01%-11.62%)and ADF contents(3.10%-5.70%)(P<0.05)of sweet sorghum silage at different stubble heights.The BC treatment group significantly increased the contents of LA(26.46%-41.83%)and AA(38.38%-74.68%)of sweet sorghum silage at different stubble heights(P<0.05).After the two were used in combination,the NDF,ADF,NH3-N content,and pH value were further reduced(P<0.05),while the contents of CP,LA,AA and aerobic stability time were significantly increased(P<0.05).(2)The bacterial community in the raw sorghum material is mainly composed of Proteobacteria(94.16-98.68%)and Pantoea(51.72%-75.27%).The relative abundance of Proteobacteria and Pantoea showed a trend of first decreasing and then increasing with an increase in the stubble height.The main bacterial genera in additive treatment group were Lactobacillus(1.18%-65.96%),Enterobacter(3.51-38.65%),Weissella(2.38%-55.74%),and Enterococcus(2.06%-77.02%).The BC treatment group increased the relative abundance of Lactobacillus at each stubble height,while the BE treatment group decreased the relative abundance of Enterobacter and increased the relative abundance of Lactobacillus at the L and H stubble heights,Enterococcus at the ML stubble height,and Weissella at the MH stubble height.(3)As the stubble height increased,the in vitro dry matter degradability(IVDMD),in vitro neutral detergent degradability(IVNDFD),AA and PA(Propionic acid)content showed an increasing trend,while the pH value and NH3-N content of the rumen fluid in vitro showed a decreasing trend.However,there was no significant difference in the MH and H stubble height(P>0.05).The IVDMD,IVNDFD,and gas production of the CE treatment group were significantly higher than those of the CON and BC treatment groups(P<0.05).The BC treatment group could significantly reduce NH3-N content of sweet sorghum silage rumen fluid(9.76%-18.0 1%)and the pH value at L and MH stubble heights(2.09%-3.54%)compared to the CON group.It also significantly increased the total volatile fatty acids(TVFAs)content(8.63%-13.39%)(P<0.05).The BE treatment group can further improved IVDMD,IVNDFD,while reducing the pH value and NH3N content of the in vitro culture fluid.In conclusion,adding Bacillus coagulans and cellulase during the ensiling process of sweet sorghum can reduce fiber content,promote lactic acid fermentation,decrease pH value and microbial diversity,inhibit harmful microorganisms,and increase in vitro digestibility.The combination of Bacillus coagulans and cellulase can further improve the quality of silage,microbial community structure,and rumen fermentation characteristics.Increasing the stubble height can also contribute to a reduction in fiber content and relative abundance of harmful microorganisms,as well as an increase in WSC and CP content,ultimately leading to improved fermentation quality.The 35 cm stubble height is recommended in practical production.