Comparative Study On Apparent Nutrient Digestibility,Rumen Fermentation Paramaters And Bacterial Structure Of High-yield And Low-yield Cows

In this thesis,rumen fermentation parameters,nutrients digestibility,quantity and diversity of ruminal bacteria of high-and low-yielding dairy cows in different lactation stages were investigated.The correlation between the lactation performance and the composition of rumen bacteria was analyzed.This study aimed to clarify the relationship between lactation performance and the composition of rumen bacteria,and provided scientific basis for scientifically raising dairy cows and improving the lactation performance of dairy cows.Two-factors experimental design was applied.The two factors were lactation performance（high yield,low yield）and lactation stage（pre-lactation,mid-lactation,and late-lactation）.The experimental animals were selected from dairy cow herd in Hohhot,Inner Mongolia.Thirty six healthy dairy cows,with similar weight,parity,body condition and feeding management were divided into 6 groups according to their lactation performance and lactation stage.Six groups were high-yield&early-lactation group（HE）,high-yield&mid-lactation group（HM）,high-yield&late-lactation group（HL）,low-yield&early-lactation group（LE）,low-yield&mid-lactation group（LM）,low-yield&late-lactation group（LL）,with 6 cows in each group.The dairy cows were raised according to the rules of herd and fed TMR.The rumen fluid was collected 6 hours after feeding to determine the number（General bacteria,R.albus,R.flavefaciens,F.succinogenes,B.fibrisolvens,S.bovis and Prevotella Ruminobacter amylophilus）and diversity of ruminal bacteria,as well as rumen fermentation parameters.TMR and fecal samples of each cow were collected to determine the nutrients apparent digestibility.The results showed that:（1）The rumen NH₃-N concentration,propionic acid,isobutyric acid concentration,DM,EE and NDF apparent digestibility of high yield dairy cows were significantly higher than those of low yield dairy cows,while concentration of acetic acid and butyric acid,as well as the ratio of acetic acid to propionic acid were significantly lower than those of low yield dairy cows（P<0.05）.（2）The numbers of R.albus,F.succinogenes and S.bovis in high-yielding dairy cows were significantly higher than those in low-yielding dairy cows（P<0.05）.（3）The rumen bacteria richness and diversity indexes of high yield dairy cows were significantly lower than those of low yield dairy cows（P<0.05）.（4）The relative abundances of bacteroides,proteobateria,prevotellaceae and muribaculaceae in high yield cows was significantly higer than those of low yield dairy cows,while the relative abundances of firmicutes,lachnospiraceae,anaerovoraceae and lachnospiraceae＿NK3A20＿group,christensenellaceae＿R7 group and acettitomaculum was significantly lower than those of low yield dairy cows（P<0.05）.（5）The relative abundance of amino acid transport and metabolism,carbohydrate transport and metabolism,transcription,cell activity,signal transduction and other functional pathways of bacteria in low yield dairy cows was significantly higher than those in high yield dairy cows（P<0.05）.（6）The concentration of BCP,butyric acid,isobutyric acid,isovaleric acid and the ratio of acetic acid to propionic acid of late lactation stage were significantly higher than those in mid lactation stage,and the concentration of propionic acid in mid lactation stage was significantly higher than that in early and late lactation stage（P<0.05）.The concentration of valeric acid in early lactation stage was significantly higher than that in middle and late lactation stage.The digestibility of DM,EE and ADF in mid lactation stage was significantly higher than that in late lactation stage（P<0.05）.（7）The number of R.albus in the early and middle lactation stage was significantly higher than that in the late lactation stage,while the relative abundance of Christensenellaceae,Lachnospiraceae＿NK3A20＿group,Christensenellaceae＿R7 group and Acettitomaculum was significantly lower than those in late lactation stage（P<0.05）.（8）The content of milk fat,milk protein and lactose of high yield dairy cows were significantly higher than those of low yield dairy cows（P<0.05）.Milk yield was negatively correlated with the relative abundance of Christensenellaceae＿R7 group,and positively correlated with the relative abundance of Muribaculaceae and Shuttleworthia.Milk fat content was negatively correlated with relative abundance of Shuttleworthia,Syntrophococcus and Unclassified Lachnospiraceae.Lactose content was negatively correlated with the relative abundance of Olsenella and Shuttleworthia.