Effects Of Partially Substituting Dietary Corn Grain With Sucrose And Lactose Onrumen Microflora And Metabolites Of Dairy Cows

This study aimed to determine the underline mechanism for the improving of milk production and milk fat synthesis of sugars on dairy cows,from the perspective of rumen microorganisms and metabolites,so as to provide a theoretical basis for the application of sugars in dairy cows.Twenty-four healthy fresh Chinese Holstein cows with similar milk yield and body conditions were used in a 4×4 Latin square experimental design,with 6 cows in each group,and the cows were in their early lactation.Four experimental phases with were 21 days each were performed with,and the rumen fluid was collected by an oral stomach-tube sampling method on the last day of each phase.16 S rRNA high-throughput sequencing technology and LC-MS metabolomics were used to investigate the effect of substituting 5% corn in dairy cows’ diets（the ratio of 55:45）with 5% sucrose,5% lactose,and an mixtion of 2.5% sucrose and 2.5% lactose（mixed group）on rumen microbial flora and the composition of rumen metabolites in dairy cows.The following results were obtained:1.Based on the 16 S rRNA high-throughput sequencing technology,a total of 18 phylum classifications and 154 genus classifications were obtained in rumen samples of dairy cows substitutied 5% corn in dairy cows’ diets with 5% sucrose,5% lactose,and an mixtion of 2.5% sucrose and 2.5% lactose（mixed group）in this experiment.Bacteroidetes,Firmicutes and Proteobacteria have the highest relative abundance at the phylum level,Prevotella₁ has the highest relative abundance at the genus level.The abundance of Spirochaetae tended to increase（P=0.093）and the abundance of Cyanobacteria and Elusimicrobia tended to decrease（P=0.052;P=0.097）in all sugar substituting groups than that in the control group.Compared with the control group,the abundance of SR1_tended to increase in lactose group（P=0.077）,and the abundance of Prevotella₁ was significantly increased in sucrose group（P<0.05）.2.Based on the LC-MS metabolomics,786 metabolites were measured and 24 metabolites were obtained after screening（VIP>1.0;P<0.05）in rumen samples of dairy cows substitutied 5% corn in dairy cows’ diets with 5% sucrose,5% lactose,and an mixtion of 2.5% sucrose and 2.5% lactose（mixed group）in this experiment.Compared with the control group,the content of 7 metabolisms in the rumen were significantly decreased（P<0.05）in all sugar substituting groups,these compounds are butyl salicylate,deoxyinosine,dodecanedioic acid,pentadecanedioic acid,α-trienol tocopherol,γ-triene tocopherol and vitamin D6.Compared with the control group,the content of 5 metabolisms e.g.uracil,thymidine,inosine,N-acetylmuramic acid and octadecanedioic acid,in the rumen were significantly decreased（P<0.05）in all sugar substituting groups.And the content of hypoxanthine was significantly decreased（P<0.05）only in sucrose group.3.According to the results of cluster analysis,dairy cows substitutied 5% corn in dairy cows’ diets with 5% sucrose,5% lactose,and an mixtion of 2.5% sucrose and 2.5% lactose（mixed group）had no significant effect on the rumen bacterial structure（P>0.05）.There is a crossover between the samples of the the control group and all sugar substituting groups.However,the replacement of 5% dietary corn with sucrose,lactose and sugarcane mixture significantly affected the composition of rumen metabolites in dairy cows（P<0.05）.The metabolite composition of all sugar substituting groups and the control group is basically separated,even all sugar substituting groups still overlapped each other.4.Twenty-two metabolic pathways were affected by substituting 5% corn in dairy cows’ diets with 5% sucrose,5% lactose,and an mixtion of 2.5% sucrose and 2.5% lactose（mixed group）of dairy cows,in which the four pathways of glutamate,leucine and isoleucine biosynthesis;β-alanine metabolism;α-Linolenic acid metabolism and linoleic acid metabolism have the most obvious effects.The above results indicate that replacing 5% corn with sucrose,lactose and the mixture can significantly affect the metabolite composition and partial bacterial abundance of rumen bacterial of dairy cows.Among them,the effect of sucrose group was greater than that of lactose group and the mixture group.