Study On The Mechanism Of Triterpenoid Saponins Regulating Rumen Metabolism Based On 16srRNA Sequencing And Metabolomics In Calves

The aim of this study was to simultaneously explore the rumen microbiota and the ruminal metabolic phenotype of calves for identifying metabolite-microbe associations under saponins' regulation.Alfalfa hay?AH?and soybean hull?SH?were set as two different fiber source control diets,either of them were treated with saponins as AHS and SHS,respectively.These four diets were fed to 24 Holstein calves?6 calves for each diet?.The experiment was conducted over 28d,with the first 7d for adaptation.Effects of triterpenoid saponins on animal performance,rumen fermentation characteristics and serum metabolism of calvesThe dry matter intake of the calves fed SHS was higher than that of the calves fed SH?P = 0.02?.The average daily gain?P = 0.07?and feed efficiency?P = 0.08?of the calves fed SHS had a tendency to be greater than those of the calves fed SH.The ruminal total VFA content in the AHS group had a tendency to be greater than that in the SH group?P = 0.07?.These results indicated that saponins have the potential ability to regulate rumen fermentation and increase the animal performance of calves.Serum NEFA concentration was lower in the AHS group than in the AH group?P<0.05?,indicating that saponin may have a role in regulating lipid metabolism in calves.Effects of triterpenoid saponins on rumen microbiome and metabolome in calves Iliumina MiSeq sequencing and ultra-high-performance liquid chromatography coupled to quadrupole time-of-flight massspectrometry?UHPLC-QTOF/MS?were used to investigate the profile changes of the ruminal microbes and metabolites,and the interaction between them.We observed a significant influence of saponins feeding in shaping the ruminal bacterial diversity and composition,with an overall dominance of bacteria of the phylum Bacteroidetes,Proteobacteria,Firmicutes,showing a greater abundance of Bacteroidetes and a lower abundance of Firmicutes in the saponins treated group than in control diet.The relative abundance of bacterial genera Prevotellaceae_YAB2003_group was increased,but Ruminococcaceae_NK4A214_group and Lachnospiraceae_NK3A20_group were decreased after calves fed saponins in both of the two basal diets.Squalene,lanosterol,3-phenylpropanoic acid,and citrulline were increased after SH supplemented with saponins.The relative abundances of predicted microbial genes using Tax4Fun was involved in amino sugar and nucleotide sugar metabolism,which was similar with the pathways of arginine and proline metabolism,purine metabolism,and pyrimidine metabolism that were enriched by differential metabolites.Moreover,in the SH based diet,a positive correlation was observed between either Prevotella₁?Bacteroidetes?or Prevotellaceae_YAB2003_group?Bacteroidetes?or Christensenellaceae_R.7_group?Firmicutes?and either citrulline,lanosterol,or squalene.In AH based diet,a significant positive correlation was observed between either Ruminococcaceae_NK4A214_group?Firmicutes?or Lachnospiraceae_NK3A20_group?Firmicutes?and hypoxanthine.These findings suggest the efficient roles of saponin in regulating ruminal microbiota and metabolic profiles in dairy calves,and the increased abundance of Prevotella₁ and Prevotellaceae_YAB2003_group might be the main factor that resulted to the improved rumen fermentation such as increased fiber digestion.Saponins might have the ability of changing ruminal lipid metabolism in calves due to the decreased abundance of Lachnospiraceae_NK3A20_group and decreased concentration of estradiol and daidzein as well as increased concentration of squalene.In summary,saponins have a role in regulating ruminal microbial community and metabolites;saponins can regulate rumen metabolic pathways and thus affect rumen environment and animal growth;the ability of saponin in regulating rumen metabolism was dietary dependence.The basic information including key microbes,metabolites,and metabolic pathways found in this study could support for the regulation of calves rumen environment by supplementing saponins to the diets.