Effects Of Bacillus Subtilis, Candida Utilis And Enterococcus Faecium On In Vitro Rumen Microbial Digestion And Metabolism And Methane Emission Of Dairy Cows

Direct-fed microbials (DFM) are dietary supplements that inhibit gastrointestinal infection andprovide optimally regulated microbial environments in the digestive tract. In the present study, threeDFM species Bacillus subtilis (BS), Candida utilis (CU) and Enterococcus faecium (EF) were chosento evaluate their effects on ruminal fermentation characteristics under different forage and TMRsubstrates by using in vitro batch culture and automated trace gas recording system for microbialfermentation. And evaluate their dosage combination effects on fibre digestibilities, ruminalfermentation characteristics and methane emission under different ratios of forage to concentrate byusing orthogonal arrays design, and screened out their optimal dosage combination. The specificexperiments as follows:The TMR (CS and MF) conditions: along with the addition levels increased in substrates, theIVDMD, NDF and ADF digestibilities, total gas production, tVFA and propionate concentrations ofDFM treatment groups were linearly increased (P<0.01), the most influence improvements appearedwhen the substrate was MF and DFM was CU. The acetate proportion and pH level in culture fluidwas significant decreased (P<0.05). The MCP concentration was significant greater and the influenceranked as CU>EF>BS. The variation tendencies of butyrate and BCVFA concentrations were not clear.Under CS condition, the optimal addition levels of BS, CU and EF were8×106,1.6×106and4×106CFU/mL, respectively; Under MF condition, the optimal addition levels of BS, CU and EF were8×106,1.6×106and4×106CFU/mL, respectively.Under forage-rich (ratio of forage to concentrate was70:30) substrate condition, adding differentdosage combinations of DFM increased total gas production, IVDMD, NDF and ADF digestibilitiesand tVFA concentration by2.8~12.3%,1.7~5.0%,2.3~20.1%,6.0~28.7%and1.8~19.1%(P<0.01),respectively. The methane proportion in total fermentation gas at incubation intervals0~6h,6~24h,24~48h and48~72h were reduced by1.6~31.1%%(P<0.01),1.0~1.7%,1.5~7.8%(P<0.01) and 6.9~20.3%(P<0.01), however the net methane production in every interval was increased whencompared to zero control after DFM addition. The optimal DFM dosage combination under thiscondition is BS:CU:EF=1:3:3, and more significant beneficial effects of DFM addition were observedwhen forage resource was Chinese wildrye hay. Under concentrate-rich (ratio of forage to concentratewas30:70) substrate condition, adding different dosage combinations of DFM increased total gasproduction, IVDMD, NDF and ADF digestibilities and tVFA concentration by9.7~43.6%,0.9~6.4%,3.6~27.6%,8.4~31.1%and2.1~19.5%(P<0.01), respectively. The methane proportion in totalfermentation gas at incubation intervals0~6h,6~24h,24~48h and48~72h were reduced by0.6~36.3%(P<0.01),1.1~1.5%,2.6~7.4%(P<0.01) and4.7~19.2%(P<0.01) after DFM addition, butthe net methane production in every interval was increased when compared to zero control. Theoptimal DFM dosage combination under this condition is BS:CU:EF=3:3:2, and more significantbeneficial effects of DFM addition were observed when forage resource was Chinese wildrye hay.In summary, the addition of BS, CU and EF could stimulate the growth of ruminalmicroorganisms and increase ruminal microbial digestibilities and improve the utilization of nutrition.The DFM addition also improved the ruminal fermentation characteristics such as VFA production,and modified ruminal microbial fermentation style. The net methane production could be increasedafter DFM addition, and such in vitro observations should be confirmed by more in vivo studies in thefuture.