| In China,straw is rich,which is an important resource for ruminants.Ruminant can use roughage feed mainly because of rumen microbial fermentation.After feeding,rumen microbes attach firstly,then a series fiber degradation activity was begun.The rumen microbial quantity and diversity attached was temporal dynamics.This study firstly compared rumen fermentation characteristics,the dynamic degradation rate and microbial adhesion condition of three sets of roughage in different degradation stages by in vitro fermentation and scanning electron microscopy(SEM)technology.Then using the nylon bag method to study the dynamic rumen degradation rate of the three groups of roughage and effective degradation rate.Finally choosing rice straw as model,analysed the microbial dynamics adhesion and degradation process.Results are shown as follows:1.Evaluation of the nutritive value and dynamic digestibility characteristics of roughage forage by in vitro fermentation.This study was conducted to evaluate the nutritive value and dynamic digestibility characteristics of roughage forages.The rice straw and wheat straw were chosen to set three groups(rice straw,wheat straw,and the mixture:50%of rice straw+50%of wheat straw).They were fermented for 72 hours in vitro.Gas production was measured at 6,12,24,36,48,60 and 72 h.Samples were collected at 0,6,12,24,48 and 72 h for the anlaysis of dynamic digestibility and fermentation characteristics.Results showed that the gas production and dry matter(DM)digestibility in three groups both increased with incubation time.Gas production of wheat straw and the mixture was higher than that of rice straw(P<0.05),and there was no significant difference between wheat straw and the mixture after 12 h of incubation.Gas production of wheat straw was significantly higher than that of rice straw and the mixture(P<0.05),and there was no significant difference between rice straw and the mixture after 24 h of incubation.Gas production ranked wheat straw>the mixture>rice straw for 36-72 h(P<0.05).After 24 hours' fermentation,DM,neutral detergent fiber(NDF)digestibility and ammonia nitrogen(NH4-N)concentration of rice straw were significantly higher than wheat straw and the mixture(P<0.05),and acetate concentration of rice straw was much more than that of wheat straw.MCP concentration were significantly lower(P<0.05).After 48 hours' fermentation,acetate of wheat straw was higher than that of rice straw(P<0.05).After 48 and 72 hours'fermentation,ADF digestibility of wheat straw was significantly higher than that of rice straw and the mixture(P<0.05).There was a large number of microorganisms colonizing within 6 h.After 24 h,a increased number of microorganisms colonizing in the straw pieces,significant degradation fragments of straw was observed.Until 72 h,the number of microorganisms remained at a high level and straw degradation was visible.In conclusion,the fermentation profiles of rice straw and wheat straw were similar and the straws were mainly degraded over 12-48 h in vitro.2.Evaluation of the nutritive value and dynamic digestibility characteristics of roughage forage by in situ fermentation.This study evaluated dynamic digestibility characteristics of roughage forages by the nylon bag method.The rice straw and wheat straw were chosen to set three groups(rice straw,wheat straw,and the mixture:50%of rice straw+50%of wheat straw).The nylon bags with substrates were incubated into the rumen of 3 similar fistulated Hostein dairy cows for 0.5,1,2,4,6,12,24,48 and 72 h.The DM,CF,NDF,ADF dynamic degradation rate and effective degradation(ED)of roughage were determined.Results showed that dry matter(DM)digestibilities in three groups were similar,and all increased with incubation time.The dry matter(DM)was rapidly degraded between 6 and 24 h.The degradation gradually slowed down from 24 to 72 h,while there was no significant degradation observed between 0.5 and 6 h.CF,NDF,ADF digestibilities were similar with the dry matter(DM).There was no significant difference in DM,NDF,CF effective degradation among the three groups(P>0.05).The effective degradation of wheat straw was significantly higher than that of rice straw and the mixture(P<0.05).DM rapidly degraded proportion of rice straw and the mixture were significantly higher than that of wheat straw(P<0.05).NDF rapidly degraded proportion of rice straw was significantly higher than that of wheat straw,while the rate of degradation of slowly degraded proportion was significantly lower(P<0.05).3.Temporal dynamics of fibrolytic bacteria colonizing rice straw in the rumenThis study was aimed to investigate and identify the fibrolytic bacteria colonizing the rice straw in the rumen.The conditions of fiber degradation and microorganisms adhesion after 0.5,6,24,72 h were detected by the technique of scanning electron microscopy(SEM)observation.The quantity and diversity of fibrolytic bacteria associated(As)and adherent(Ad)with rice straw were investigated by real-time PCR and Miseq sequencing of 16S rRNA genes.Results showed that(1)There was a large number of microorganisms colonizing within 0.5 h.After 6 h,a increased number of microorganisms colonizing in the straw pieces,significant degradation fragments of straw was observed.After 24 and 72 h,the number of microorganisms remained at a high level and straw degradation was visible.(2)Quantification of attached fibrolytic bacteria showed that the number of bacteria in As fraction was significantly(P<0.05)lower than Ad fraction.(3)Community analysis of fibrolytic bacteria showed that high proportion of unclassified bacteria were attached to rice straw and Prevotella,Ruminococcus and Butyrivibrio were dominant classified genera in both As and Ad fraction.Bacterial community in As fraction remained relatively stable over the incubation,while a significant shift in Ad fraction was observed after 6 h incubation.The shift resulted in significant(P<0.05)reduction of Anaerostipes,Blautia,Butyrivibrio,Coprococcus,Desulfovibrio,Prevotella,Pseudobutyrivibrio,Ruminococcus and Succiniclasticum,and significant(P<0.05)increase of Clostridium,Dehalobacterium and Oscillospira.Correlation analysis suggested that all of the fibrolytic bacteria that were highly(P<0.001)related to fiber degradation in Ad fraction was unidentified so far.Fibrobacter succinogenes and Ruminococcus spp.in As fraction were highly(P<0.001)related to the fiber degradation.In conclusion,our results demonstrated the temporal colonization of rice straw by fibrolytic bacteria in the rumen,but the tightly attached fibrolytic bacteria that were highly related to the degradation of rice straw were unidentified and thus identification and functional analysis of these bacteria should be further investigated. |
PDF Full Text Request