Effects Of Subacute Ruminal Acidosis On Nutrient Digestibility And Roughage Degradation In The Rumen Of Dairy Cows

The purpose of this study was to explore the effect of subacute ruminal acidosis(SARA)on nutrients digestibility,ruminal fermentation and roughage digestibility in lactating dairy cows.The content was divided into three parts:1.Effects of SARA on the apparent digestibility of nutrients and rumen fermentation in dairy cowsTo explore the effect of SARA on nutrients digestibility,rumen fermentation parameters in dairy cows,12 Holstein cows were randomly divided into two groups,namely the control group(CON,n = 6)and the SARA group(SARA,n = 6).The CON group was fed total mixed rations with F:C = 6:4,while the SARA group was fed total mixed ration with F:C = 4:6.The experiment consisted of 7 days of pre-feeding period and 21 days of formal experiment period.TMR,rumen fluid and rectal feces samples were collected during formal experiment period.The results showed that,compared with the CON group,SARA significantly reduced the rumen p H(P < 0.001),acetate concentration(P < 0.001)and the ratio of acetate to propionate(P < 0.001),but significantly increased the total VFA concentration(P =0.010),propionate concentration(P < 0.001)and the proportion of propionate(P <0.001).Meanwhile,the SARA group of the total VFA concentration(P = 0.020)in feces significantly increased.Furthermore,the results of the apparent digestibility of nutrients in feces showed that the SARA group of the apparent digestibility of DM(P< 0.001),CP(P = 0.001),NDF(P < 0.001),ADF(P < 0.001)and OM(P < 0.001)significantly reduced compared with the CON group.The results showed that,SARA has significant effect on rumen fermentation in dairy cows,reducing the rumen p H,acetate concentration and the ratio of acetate to propionate,and significantly increasing propionate concentration and the total VFA concentration.In addition,SARA significantly reduced the apparent digestibility of dietary nutrients in dairy cows.2.Effects of SARA on the dynamic degradation characteristics of alfalfa and leymus chinensis in rumen of dairy cows bsaed on nylon bag technologyThe purpose of this chapter was to study the effect of SARA on the dynamic degradation characteristics of alfalfa and leymus chinensis in rumen of dairy cows.We selected three health Holstein cows as the CON group and three Holstein cows suffering from SARA as the SARA group in the experiment.The results showed that,SARA significantly effected the effective degradation rate of DM(P = 0.006),CP(P< 0.001),NDF(P = 0.003),ADF(P = 0.005)and OM(P = 0.007)in alfalfa compared with the CON group.Furthermore,SARA also significantly effected the effective degradation rate of DM(P =0.015),CP(P = 0.011)and OM(P = 0.021)in leymus chinensis,but the effective degradation rate NDF(P = 0.095)and ADF(P = 0.092)has no significant effect compared with the CON group.Thus,the results showed that SARA has significant effect on the degradation process of roughage by rumen microorganisms.3.Effects of SARA on the composition and structure of rumen microflora adhered to alfalfa and leymus chinensisThe purpose of this chapter was to explore the effect of SARA on the composition and structure of rumen microflora adhered to alfalfa and leymus chinensis.The experiment design was the same as experiment two.Taking alfalfa and leymus chinensis in nylon bags at each time point,then extracting microbial genomic DNA and sequencing based on 16 S r RNA amplification technology.The principal coordinates analysis results showed that bacterial communities adhered to alfalfa and leymus chinensis were significantly separated between the CON and SARA groups.The alpha diversity results showed that rumen incubation time significantly effected the Observed OTUs index(P = 0.006)and Shannon index(P < 0.001)of bacterial communities adhered to alfalfa in two groups.Compared with the CON group,SARA significantly decreased the Observed OTUs index(P < 0.001)and Shannon index(P< 0.001)of bacterial communities adhered to alfalfa.At the phylum level,SARA significantly increased the relative abundance of Proteobacteria(P = 0.009)and Cyanobacteria(P = 0.029)compared with the CON group.At the genus level,SARA significantly increased the relative abundance of four genera and significantly decreased the relative abundance of three genera compared with the CON group.Similarly,leymus chinensis as the inoculum,SARA also significantly decreased the Observed OTUs index(P < 0.001)and Shannon index(P < 0.001)compared with the CON group.At the phylum level,SARA significantly increased the relative abundance of Proteobacteria(P < 0.001),Spirochaetae(P = 0.029)and Actinobacteria(P = 0.019)compared with the CON group.At the genus level,SARA significant increased the relative abundance of one genus,but significantly reduced the relative abundance of seven genera compared with the CON group.The results showed that SARA has significant effect on the structure and relative abundance of rumen microflora adhered to roughage surface.