Effects Of L-Lactic Acid And D-Lactic Acid On The Fermentation In Rumen Simulation Continuous Cultural System (Rusitec)

Studies have shown that lactic acid is an important intermediate product of feed metabolism in the rumen,and its accumulation in the rumen is the main cause of rumen acidosis.The silage for feeding ruminants must rely on a large amount of lactic acid produced by raw material fermentation to inhibit the proliferation of harmful substances.However,at present,no research has focused on the effect of the content of L-and D-lactic acid in the diet on rumen metabolism of ruminants.Therefore,this experiment intends to take beef cattle and whole plant silage corn as the research object,and use the double outflow artificial rumen simulation technology to study the determination method of L-and D-lactic acid in whole plant silage corn and its effect on beef cattle rumen fermentation,so as to provide scientific basis and technical support for the scientific application of silage in ruminant production.Experiment 1 Determination of L-,D-lactic acid concentration in whole plant silage corn feedThe contents of lactic acid,D-lactic acid and L-lactic acid in silage made of 20 different whole plant silage corn in different regions of China were determined by ultra-high performance liquid chromatography.The accuracy of parallel reaction detection method by mass spectrometry was improved,and a liquid chromatography-mass spectrometry method for the determination of silage was established.In the sample,the concentration of L-lactic acid is 4.28±1.41%,the concentration of D-lactic acid is 1.34±0.38%,the concentration of lactic acid is 5.62±1.72%,and the L/D ratio is 3.18±0.77.The minimum detection limit(LOD)of this sample is less than 31.25μmol/L,the lowest limit of quantitation(LOQ)was63.44μmol/L;The linear coefficient(R~2)of the sample is 0.9996,indicating that there is a good linear correlation between the chromatographic peak area and the compound concentration.The recovery of lactic acid sample in silage is 81.04%,indicating that this method can achieve the purpose of rapid determination of L-lactic acid and D-lactic acid in the sample.Experiment 2 Effect of L-,D-lactic acid content on fermentation in continuous culture rumen simulation system in vitroThe uniform experimental design method was adopted in the experiment.Two factors of L-lactic acid and D-lactic acid were selected as the test factors of uniform design.Each factor was set at 6 levels and divided into 6 treatment groups(the addition amount of L-lactic acid and D-lactic acid(%)were 0/0.6,2/4.8,4/0.3,6/2.4,8/0 and 10/1.2 respectively).The experiment was carried out in 6 fermentation tanks of double external flow continuous rumen simulation system.The total experimental period was 21 days and was divided into 3stages(each stage was regarded as a repetition),The period is(pre-test period of the first 3days and test period of the next 4 days).The experimental results analyzed the data of the established regression mathematical models of target parameters(dependent variables)and L-,D-lactic acid(independent variables)through various analysis methods,and predicted the critical value of exogenous addition of L-,D-lactic acid in subacute ruminal acidosis.The results showed that with the increase of L-lactic acid and D-lactic acid in the diet,the p H,NH3-N concentration,MCP content,the degradation rate of DMD,NDF and CP and the number of protozoa in the rumen system decreased significantly(or decreased)(P<0.01);The contents of lactic acid,tvfa,acetic acid,propionic acid and butyric acid increased significantly(P<0.01);The concentrations of D-lactic acid,butyric acid,isobutyric acid and isovaleric acid increased significantly with the increase of D-lactic acid(P<0.01);The concentration of valeric acid and CP degradation rate decreased significantly with the increase of D-lactic acid(P<0.01);The concentration of L-lactic acid,the degradation rate of ADF and EE increased with the increase of L-lactic acid content(P<0.01);There was a significant correlation between rumen lactic acid,L-lactic acid and D-lactic acid and rumen p H,NH3-N,total volatile fatty acids,acetic acid,propionic acid,isobutyric acid,valeric acid,isovaleric acid,protozoa number,MCP and nutrient degradation rate(r=-0.926～0.863,P<0.05).The prediction results of regression equation show that when the content of L-lactic acid was 5%,the content of D-lactic acid was 2%or only 3%of D-lactic acid was added,the rumen began to enter Sara state.