Study On Milk Odd-and Branched-chain Fatty Acids As Marker Of MCP

The purpose of this study was to explore the relationship between OBCFA and MCP,so as to provide a new method for more efficient prediction of MCP,and further clarify the mechanism and feasibility of OBCFA as a marker.Test?:Study on the effects of F:S on OBCFA,ruminal fermentation parameters,MCP and ruminal bacterial populations in vitro fermentation and correlation.Different ratios of fiber and starch were fermented in vitro,which were F:S=0:100,25:75,50:50,75:25 and 100:0,respectively.The p H,volatile fatty acids?VFA?,ammoniacal nitrogen?NH₃-N?,MCP and OBCFA were measured at 6,12,18 and 24 h and the changes in the microflora were analyzed by high-throughput technology.The results showed that there were significant differences in the content of OBCFA under different F:S?P<0.05?.At 24 h of fermentation,the content of iso C15,anteiso C15 and C17 were higher in the group of F:S=75:25,while anteiso C17and acetate were higher in the group of F:S=50:50.The C15 and propionate were highest in the group of F:S=100:0,while the iso C16,iso C17 and MCP content were highest in the group of F:S=0:100.With the increase of starch content,the concentration of NH ₃-N decreased,while the concentration of TVFA increased?P<0.05?.When the F?50%,Proteobacteria occupied a larger proportion,and the relative abundance of Fibrobacteres was significantly higher in the group of F>50%?P<0.05?.Test II:Study on the effect of the infusion of NH₄HCO₃ on OBCFA in rumen and milk,ruminal fermentation parameters and MCP and correlation.Three Holstein lactating cows with permanent fistula were selected,and three doses of NH₄HCO₃?0,112 and 224 g/d?were used for rumen perfusion in a 3×3 Latin square design.Rumen samples were collected every 2 h within 12 h,and the p H,VFA,NH ₃-N,MCP and OBCFA were measured.The results showed that the contents of iso C14 and iso C17 and TIFA in rumen increased significantly as the concentration of NH₄HCO₃ increased?P<0.05?,and the content of MCP tended to increase?P=0.06?,but there no significant effect of the concentration of NH₄HCO₃ on p H,NH₃-N and VFA?P>0.05?.There was strong correlation between OBCFA in rumen?or milk?and ruminal fermentation parameters,MCP and bacteial populations.Among them,Bacteroidetes was negatively correlated with iso C17 and C17?r=-0.31?-0.54,P<0.05?,Proteobacteria was positively correlated with iso C16and anteiso C15?r=0.47,P<0.05?,Firmicutes was negatively correlated with iso C15,anteiso C15,iso C17 and anteiso C17?r=-0.30?-0.35,P<0.05?,Fibrobacteres was positively correlated with C15and its isomers?r=0.43?0.80,P<0.05?.C17 in rumen was correlated with p H and NH₃-N,C15 was significantly correlated with acetate,iso-fatty acids were significantly correlated with propionate?P<0.05?.Branched-chain fatty acids were positively correlated with MCP?r=0.44?0.79,P<0.05?.While anteiso C17 in milk was significantly negatively correlated with p H?r=-0.76,P<0.05?,and C17 and its isomers were positively correlated with NH₃-N?r=0.64?0.84,P<0.05?.Anteiso C15 was negatively correlated with acetate?r=-0.89,P<0.05?and positively correlated with MCP?r=0.78,P<0.05?.In conclusion,the conclusions of this study are as follows:?1?The F:S have significant effects on OBCFA,rumen fermentation parameters,MCP and microflora.?2?Rumen perfusion with high concentration of NH₄HCO₃ can significantly increase the content of iso C14 and iso C17 and TIFA in the rumen,and tend to increase the content of MCP.?3?The ruminal OBCFA is significantly correlated with the relative abundance of bacterial,and can be used as a rumen bacterial marker.?4?Anteiso C15 in rumen and milk are significantly related to MCP and can be used to predict MCP.