The Correlation Of Rumen Bacterial Community And Nitrogen Utilization Efficiency Of Dairy Cows

The shortage of protein-feed resource and heavy dependence on import are the key factors that limit the development of livestock industry in china.Currently,many studies have been conducted to improve the protein utilization efficiency of dairy cows,but the nitrogen utilization efficiency（NUE）is only 25%.NUE with low level not only wastes feed nitrogen source,but also pollutes the environment.Therefore,to improve NUE is the focus of scientific research.In recent years,researchers have clarified the important role of rumen microorganisms in the digestion,nutrition absorption and production performance of dairy cows.However,there are still few studies on the cor-relation between rumen microbial community and NUE of dairy cows.Researches have shown thatΔ¹⁵N can overcome individual differences and effectively evaluate NUE.Therefore,the experiment revealed the individual physiological factors affecting the NUE of Holstein dairy cows by analyzing the production performance,rumen fer-mentation and blood biochemical;according toΔ¹⁵N,MPY as NUE parameters,the group was divided into HE＿HP,ME＿MP,LE＿LP,compared and screened out the ru-men bacteria composition of dairy with different NUE by 16S rRNA.Experiment 1:Production performance,rumen fermentation and blood biochemical effecting on NUE of Holstein dairy cows.Two-hundred and eighty-four healthy dairy cows in second lactation between 24 and 77 days in lactation were filtered and record-ed the composition of diet,milk yield,days in lactation,and collected milk,rumen fluid and blood.Thereby,we tested milk components,rumen fermentation parameters,plasmaΔ¹⁵N and blood biochemical parameters.The results were as follows:（1）Days in milk（DIM）,milk yield（MY）,milk protein（MP）were positively corre-lated with milk protein yield（MPY）（P<0.01）.Moreover,MY and MPY were nega-tively correlated withΔ¹⁵N（P<0.01）。（2）Acetate/propionate,isobutyrate and valerate were positively correlated withΔ¹⁵N（P<0.01）,but rumen fermentation were not correlation with MPY（P>0.05）.（3）Non-esterified fatty acid（NEFA）,Uric acid（UA）,purine derivatives（PD）were negatively correlated withΔ¹⁵N（P<0.05）,plasma urea nitrogen（PUN）,free amino ac-ids（FAA）,UA and PD were correlated with MPY（P<0.05）.Experiment 2:Effects of composition and structure of rumen bacteria on NUE of dairy cows.The 21 dairy cows were screened out from 284 Holstein dairy cows according toΔ¹⁵N and MPY,and divided into HE＿HP（n=7）,ME＿MP（n=7）,LE＿LP（n=7）.The results were as follows:（1）The Shannon index and Simpson index of LE＿LP were higher than HE＿HP,ME＿MP indicated that rumen bacteria had high diversity in LE＿LP（P<0.05）;PCo A showed the composion of rumen bacteria was different between HE＿HP and LE＿LP（P<0.01）.（2）At phylum level,Bacteroidetes,Firmicutes,Proteobacteria are common domi-nant phylum.The relative abundance of Firmicutes in HE＿HP,ME＿MP was lower than in LE＿LP（P<0.01）,but Proteobacteria was higher in LE＿LP（P<0.01）.（3）At family level,Prevotellaceae,Succinivibrionaceae,Lachnospiraceae are common dominant family.The relative abundance of Succinivibrionaceae in HE＿HP,ME＿MP was higher than in LE＿LP（P<0.01）.（4）At genus level,Prevotella,Succinivibrionaceae＿UCG＿001 are common do minant genus.The relative abundance of Succinivibrionaceae＿UCG＿001,uncultur ed Selenomonadaceae in HE＿HP,ME＿MP was higher than in LE＿LP analysed b y LEf Se（P<0.05）.But the abundance of Clostridia＿UCG＿014,Lachnospiraceae＿NK3A20＿group,Desulfovibrio,Saccharofermentans,Christensenellaceae＿R＿7＿gro up,Bacilli＿RF39 were lower in HE＿HP,ME＿MP（P<0.05）.（5）Based on correlation analysis of the bacteria and NUE,Succinivibri-onaceae＿UCG＿001、uncultured Selenomonadaceae were positively correlated with MY and MPY were negatively correlated withΔ¹⁵N（P<0.05）;Clostridia＿UCG＿014、Desulfovibrio,Saccharofermentans,Bacilli＿RF39 were negatively correlated with MY,MPYwere positively correlated withΔ¹⁵N（P<0.05）.In conclusion,the NUE of dairy cows was affected by physiological factors included DIM,VFA,NEFA,PUN,FAA,PD.There are differences in the rumen microbes of dairy cows with different NUE,The bacteria that promote NUE inc luded:Succinivibrionaceae＿UCG＿001、uncultured Selenomonadaceae,the bacteria are unfavorable to NUE included:Clostridia＿UCG＿014,Desulfovibrio,Saccharof ermentans.