Effects Of Mannan Oligosaccharides On Rumen Fermentation And Milk Fat Regulation Of Low Milk Fat Dairy Cows Induced By High Concentrate

In this study,4 Chinese Holstein dairy cows with the late lactation and the same parity were selected.The whole test period was 56d and divided into three stages that named,Test Ⅰ,Test Ⅱ and Test III.The experimental dairy cows were fed with basic diet as control group,and the test period was 14d in Test Ⅰ.It was to construct the low-fat dairy cow model in Text Ⅱ.The test cows were perfused with corn meal on basal diet,in order to make dietary starch content reached 27%.The test period was 28d in the Test Ⅱ.The test cows were perfused with corn meal on the basic diet,so that the cow’s dietary starch content was 27%,and supplemented with 200g MOS.The test period was 14d in the Test Ⅲ.This study investigated and analyzed the effects of supplementing MOS on rumen fermentation parameters,rumen flora,CAZy and serum indicators of low-fat dairy cows induced by high concentrate.The aim was that explored the mechanism of MOS in milk fat regulation of low-fat dairy cows,and provided more theoretical for application of MOS in dairy cows.The test results are as follows:MOS increased the pH value of rumen（P<0.01）,and increased the content of acetic acid and ethylene-propylene ratio（P<0.05）,and decreased the content of propionic acid in the rumen（P<0.05）,and increased the content of MCP（P>0.05）.There was no significant effect on NH3-N and butyric acid（P>0.05）.MOS increased the milk fat percentage of low-fat dairy cows.MOS had effect on the structure of rumen bacteria in low-fat cows induced by high concentrate.At the phylum level,MOS could reduce the abundances of Bacteroidetes（[P<0.05）,Spirochete(P>0.0 and Actinobacteria（P>0.05）compared with Text Ⅱ.The abundance of Firmicutes was increased（P<0.05）,and significantly higher than that of control group（P<0.05）.The abundance of Fibrobacteres was significantly increased that compared with Text Ⅱ and control group（P<0.01）.At the genus level,the abundance of Prevotella₁ was reduced（P<0.01）;the abundances of Prevotella₇,Lactobacillus and Lactococcus were reduced（P<0.01）.The abundances of Prevotella_UCG-001 and_UCG-003 were increased.And the abundance of Prevotella_UCG-001 was significantly higher than control group（P<0.01）.The abundance of Prevotella_UCG-003 was significantly higher than that of control group and Text Ⅱ（P<0.01）.The abundance of Succinclasticum was significantly increased（P<0.05）.Functional prediction of the rumen flora revealed that low-fat dairy cows supplemented with MOS reduced the abundance of the flora involved in starch and sucrose metabolism.MOS changed the composition ratio of rumen microbial CAZy in low-fat dairy cows.MOS could up-regulated the abundances of GH48（P<0.01）,CBM2（P<0.05）,CBM3（P>0.05）and AA10（P<0.01）which the fiber-degrading enzymes in the rumen of low-fat dairy cows.And it could down-regulated the abundance of GH24 which degraded starch（P<0.01）.The abundances of GH43 and GH28 which were hemicellulose-degrading enzymes were down-regulating（P<0.05）.And there is no mitigation effect on down-regulating GH5 that was fiber-degrading enzyme.MOS could significantly reduce the content of INS and increase the content of NEFA in the blood of low-fat dairy cows（P<0.05）.It couldn’t alleviate the decrease of albumin and IgG,and the content of ALB and IgG in Text Ⅲ was extremely lower than that of control group（P<0.01）.The content of IL-6,IgA and IgM in blood of low-fat dairy cows was increased（P>0.05）.The content of TNF-a was decreased（P>0.05）.There was no significant effect on SOD,T-AOC,BHBA and GLU（P>0.05）.In summary,the addition of MOS to low-fat dairy cows induced by high concentrate can improve the rumen fermentation mode,increase the abundance of cellulose degrading bacteria by increasing the abundance of some rumen-degrading bacteria,and reduce the abundance of some starch-degrading bacteria.Down-regulating the abundance of starch-degrading enzymes has a positive effect on stabilizing rumen pH;increasing the content of acetic acid in the rumen,reducing the content of propionic acid,increasing the milk fat percentage of low-fat dairy cows;inhibiting the proliferation of some pathogenic bacteria,To some extent,it improves the immunity of the cow’s body;but it also down-regulates the abundance of some hemicellulose degrading enzyme genes.