Effect Of Lactic Acid Bacteria And Fibrolytic Enzymes On The Fermentation Quality Of Switchgrass Silage And Mechanism Involved

Switchgrass (Panicum virgatum L.), a C4-grass native to North America, has great potential as a livestock feed when either grazed or conserved as hay or silage. Desirable traits include its high biomass yield potential, adaptability to marginal soil, and perennial growth habit. Low concentration of water soluble carbohydrate and high concentration of NDF, as well as the low number of lactic acid bacteria adhered are principal factors which influence the potential of ensilling C4grasses. The objective of this study was to determine the effect of different lacic acid bacteria and different exogenous fibrolytic enzymes, as well as the combination of lactic acid bacteria and fibrolytic enzymes on the fermentation quality of switchgrass silage and mechanism involved. Switchgrass (lowland ecotype) harvested at vegetable stage (mid-June) was cut into1-2cm and treated with different additives, then ensiled derectly in silos for30. The main details and results are as follows:(1) A stable lactic acid bacteriacommunity from switchgrass silage named SGL was obtained by continuous restricted subcultivation in the MRS broth. The microbial composition of SGL was stable and mainly included L.nantensis (78.78%), L.plantarum (7.92%), L.pantheris (5.27%), Bacillus coagulans (4.41%) and Lactococcus lactic (3.31%). The pH value of the MRS inoculated with SGL dropped to3.7, and the yield of the lactic acid reached26g/L after24h cultivation. The best supplementation of yeast extraction for SGL was20g/L. When the elemental nitrogen ratio of (NH4)2SO4to yeast extract was1:4, the growth and lactic acid production were no significant difference with0:5(P>0.05).(2) Freshly chopped switchgrass was untreated or treated with L. buchneri, L.plantarum, L.brevis and LAB community SGL. Each inoculants was added to achieve1D600/kg of fresh forage. Overall, inoculation with lactic acid bacteria improved the relative aboundance of Lactobacillus and reduced the relative aboundance of Enterobacter, increased the concentration of lactic acid, lowered the pH value, decreased the concentrations of butyric acid and NH3-N, increased the concentration of crude protein, and improved the recovery rate of dry matter. Among four inoculants, L.brevis was most efficient on promoting fermentation, followed by LAB community SGL, the third one was L.plantarum, and the effect of L. buchneri was not significant.(3) Freshly chopped switchgrass was untreated or treated with fibrolytic enzymes,1) C9748,2) Xiaoguo and3) V2010. Each enzyme preparation was added to achieve0.4g/kg of dry matter. Overall, treatments with fibrolytic enzymedecreased the concentration of NDF, accelerated the decline of pH value of the silages during fermentation AND lowered pH value of the end silages, increased the concentration of lactic acid and decreased the concentrations of butyric acid and NH3-N. Although in all treatment, the relative aboundance of Lactobacillus improved, Enterobacter was not inhibited and was still the dominant bacteria. Among three treatments, C9748was most efficient on the fermentation.(4) Freshly chopped switchgrass wastreated with the combination of LAB and fibrolytic enzyme,1) SGL and C9748and2) SGL and Xiaoguo, the untreated or treatments with SGL, C9748andXiaoguo alone were as controls. Overall, the silage quality of treatments with LAB plus fibrolytic enzyme was better than treatments with LAB or fibrolytic enzyme alone, and meeted the state "excellence level". pH value of SGL+C9748and SGL+Xiaoguo were lowered to4.0and4.2, butyric acid was not detected, and the concentrations of lactic acid increased by3.72-fold and1.82-fold compared to SGL alone, respectively. The effect of SGL+C9748was best, concentration of crude protein increased by10.61%compared to SGL alone, and concentration of cellulose decreased by4.69%and the concentration of water soluble carbohydrate increased by81.82%compared to C9748alone.(5) An artificial rumen system was conducted to investigate the effect ofinoculated corn silage. Overall, in vitro dry matter degradation (IVDMD), pH value, NH3-N and VFAs production were different among inoculated substrates. Combinating LAB community and fibrolytic enzyme improved the IVDMD, promoted the proteolysis, and enhanced the rumenfermentation of switchgrass silage. In addition, the effect of the combination was better than LAB or fibrolytic enzyme alone, and LAB alone was better than fibrolytic enzyme alone.