Effects Of Subacute Rumen Acidosis On The Absorption Of Volatile Fatty Acids In Rumen Epithelium Of Dairy Goats And Its Mechanism Research

About 50%-85%of the VFA produced by rumen fermentation is directly absorbed,transported and metabolized by the rumen epithelium,which plays a key role in the regulation of the body's energy balance.However,the effect of SARA on VFA absorption in rumen epithelium is still unclear.In this study,dairy goats were used as animal models to study the effect of SARA on the absorption rate of acetic acid,propionic acid and butyric acid and their expression of related genes to absorption and metabolism in rumen epithelial cells by rumen perfusion technique and molecular biology technique,so as to explore the mechanism of SARA's effect on VFA absorption and metabolism in rumen epithelium.1.Effect of SARA on VFA absorption rate in rumen epitheliumIn this experiment,a completely randomized design was used.12 transgenic Saanen dairy goats aged 3 years old and weighing 62.13±4.76 kg were randomLy divided into two groups,namely the control group and the SARA group.The dairy goatts in control group were fed a diet with NFC/NDF=1.15 and those in the SARA group were fed four experimental diets with NFC/NDF of 1.15,1.49,2.12 and 2.66 in turn to induced SARA.Each of these diets was fed for 15 days to induce SARA.Six animals(n=3 in the control group and n=3 in the SARA group)were used.The rumen relative steady state was established by continuous feeding.The effects of SARA on VFA production rate,outflow rate and absorption rate in the rumen epithelium were studied by initiating-continuous perfusion of acetic acid,propionic acid and butyric acid.The results showed that:(1)compared with the control group,the rumen pH value in the SARA group was lower than 5.5 for the duration of 4.71 h/d.The concentration of acetic acid and A/P in the rumen fluid in the SARA group decreased significantly(P<0.05),and the concentrations of propionic acid,butyric acid and TVFA increased significantly(P<0.05).(2)In the SARA group,acetic acid production rate and the outflow rate decreased significantly and absorption rate increased significantly(P<0.05).The production rate,outflow rate and absorption rate of propionic acid and butyric acid increased significantly(P<0.05),but only the absorption rate of butyric acid increased significantly(P<0.05).These results indicated that SARA changes the VFA production rate,flow rate and absorption rate of the rumen epithelium.2.Effect of SARA on mRNA expression of VFA absorption and metabolism related genes in rumen epithelialExperimental animals and diets are the same as experiment one.The 6 Experimental animals(n=3 in the control group and n=3 in the SARA group)were slaughtered.The rumen epithelial tissue was collected,and the mRNA expression levels of VFA absorption and metabolism-related genes in rumen epithelial cells were detected by real-time quantitative PCR.The results showed that the mRNA expression levels of VFA absorption genes MCT-1,NHE1,NHE3 and DRA(P<0.05)were significantly increased(P<0.05)and the mRNA expression levels of VFA metabolic genes ACSS1 and ACSS3 were significant decreased(P<0.05),and The mRNA expression levels of ACSS2,HMGCS1,HMGCS2 and HMGCR were significantly increased(P<0.05)in rumen epithelial cell of SARA group.These results indicated that SARA affects mRNA expression of VFA uptake and metabolism related genes in rumen epithelium3.Effect of SARA on the protein expression of VFA absorption and metabolism related genes in rumen epithelialExperimental animals,diets and designs are the same as experiment two.The protein expression of VFA uptake and metabolism-related genes in rumen epithelial cells was detected by Western blot.The results showed that SARA up-regulated the protein expression levels of VFA uptake genes NHE1,NHE3,NHE4,MCT-2,AE2 and ATP1A1(P<0.05),and those of VFA metabolic genes ACSS2,ACSS3,HMGCL and ACAT1(P<0.05)in rumen epithelial cells.These results indicated that SARA affects the expression of VFA absorption-related genes in rumen epithelium.SARA significantly reduced the rate of acetic acid production and the flow rate.The propionate and butyric acid,on the other hand,the absorption rates of acetic acid,propionic acid and butyric acid increased significantly.The absorption rate of acetic acid and propionic acid increased,only the absorption rate of butyric acid.Significantly increased,which was closely related to the rumen pH value,mRNA and protein expression of VFA absorption and metabolism in rumen epithelial cells.