| In this study,combining with animal experiment,the techniques including in vitro and in situ were used to investigate the rumen degradation characteristics of two different quality forages,and to explore its effect on rumen fermentation and metabolism of dairy cows.This thesis includes three sections as follow:1.Study on nutritional value of two different quality forages in vitroThis experiment aims to evaluate the impact of two different quality forages(AH vs CS)under equal concentrate diets on rumen fermentation in vitro.The results showed that,after 24h gas production,NH3-N,acetic acid,propionic acid,isovaleric acid,valeric acid and total volatile fatty acids concentration of AH group were significantly higher than CS group(P<0.05))while the pH value(P<0.001)and the lactate concentration(P=0.029)of AH group were significantly lower than CS group;and no significant changes(_P>0.05)were observed in the microbial protein,isobutyric acid and butyric acid concentrations and A:P between the two groups.In summary,our data reveal that the nutritive value of alfalfa hay is higher compared with corn stover.2.Comparison of the ruminal degradation characteristics of two different quality forages in situIn this study,three ruminally cannulated holstein dairy cows were choosed and nylon-bag technique was used to evaluate the rumen degradation characteristics of alfalfa hay and corn stover and their effective degradabilities of DM,CP,NDF and ADF.The results showed that the effective degradabilities of DM and CP in alfalfa hay were more than 50%and were significantly higher than corn stover(P<0.05),and the effective degradabilities of NDF and ADF in alfalfa hay were more than 30%and were significantly higher than corn stover(P<0.05)In summary,these results reveal that alfalfa hay has faster and higher degradation rate compared with corrn stover,indicating alfalfa has a higher feeding value for dairy cattle compard with the corn stover.3.Effect of two different quality forages on rumen fermentation of dairy cowsThis study aims to investigate the effect of different quality forages on rumen metabolism of dairy cows based on GC-MS,conbined with multivariate analysis.Twenty healthy multiparous Holstein dairy cows were blocked based on milk yield and weight and were randomly assigned to two groups(AH vs CS).Diets were isonitrogenous,with a concentrate-to-forage ratio of 55:45,after a 56-d feeding,rumen fluid was collected from all cows to characterize the rumen fermentation and the metabolites using metabolomics method.The results showed as followed:The pH and lactic acid level of the cows were not affected by forage quality(P>0.05),and the concentration of NH3-N in CS was significantly higher than AH(P=0.004),but the concentration of MCP was significantly lower than AH(P=0.010).No significant difference was found in the concentration of acetic acid,propionic acid,isobutyric acid,butyric acid,total VFA and A:P between AH and CS diets(P>0.05),however,the concentrations of iso valerate and valerate in AH showed significantly higher than CS(P<0.05).PCA and OPLS-DA found that the rumen fluid samples in AH and CS could be clustered and distinguished by the forages.There was 39 metabolites that differed significantly between diets AH and CS(VIP>1,P<0.05),among 39 dissimilar metabolites in the rumen fluid,36 metabolites was higher for diet AH than CS,and these potential differences metabolites include amino acids,organic acids and fatty acids.Pathway analysis showed the effect of AH on rumen metabolism mainly related with amino acid and fatty acid metabolism pathways.These results reveal that the effects of two different quality forages on rumen fermentation and amino acids metabolism are significant difference. |
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