Effect of supplementation of inulin in dietary on lactation performance, rumen fermentation, ruminal microbial profile and metabolites in dairy cows

Background Inulin is a kind of fructo-oligosaccharide (FOS) derived mainly from Jerusalem artichoke and chicory tubers, which is also a soluble dietary fiber. Inulin has become a scientifically proven prebiotic product with satisfactory effects in improving the structure of intestinal flora, regulating blood lipid and glycemia, etc., in humans and monogastric. However, unlike monogastric animals, ruminal microbes are the largest microbiota in ruminants. The microflora profile and metabolism activity in the rumen are closely related to the health of dairy cows. This study investigated the effects of inulin on rumen fermentation parameters, ruminal microbiome and metabolites, as well as lactation performance and serum indexes in dairy cows. A total of 16 Holstein dairy cows with similar body condition were randomly divided into two groups (n = 8 per group), with inulin addition at 0 and 200 g/d per cow, respectively. Experiment was lasted for 6 weeks including 1 week of adaptation period and 5 weeks of treatment period. At the end of the experimental period, the milk, serum and rumen fluid were sampled and analyzed. The rumen microbiota and metabolites were analyzed via 16S rRNA sequencing and untargeted metabolomics, respectively. Results The supplementation of inulin (200 g/d per cow) increased the milk yield (P = 0.001), milk protein (P = 0.032), lactose rate (P = 0.004) and the proportion of saturated fatty acids (SFA) in milk (P < 0.001), while decreased the proportion of unsaturated fatty acids (USFA) (P = 0.041). Rumen pH (P = 0.040) and concentration of NH3-N (P = 0.024) were decreased, however, acetate (P < 0.001), propionate (P = 0.003), butyrate (P < 0.001) and lactic acid (LA) (P = 0.043) were increased. The total cholesterol (TC) (P = 0.008) and triglycerides (TG) (P = 0.01) in serum were also reduced. Additionally, the inulin addition elevated the relative abundance of several beneficial symbiotic and short-chain fatty acids (SCFA)-producing bacteria, such as Muribaculaceae (FDR-adjusted P < 0.01), Acetitomaculum (FDR-adjusted P = 0.043), and Butyrivibrio (FDR-adjusted P = 0.036) etc., meanwhile elevated the levels of L-Lysine (FDR-adjusted P = 4.24 × 10− 3), L-Proline (FDR-adjusted P = 0.0158), L-Phenylalanine (FDR-adjusted P = 0.027), etc. By contrast, several pathogens and ruminal bacteria abundant in high-fat diets, such as Escherichia-Shigella (FDR-adjusted P = 0.022), Erysipelotrichaceae__UCG-004 (FDR-adjusted P < 0.01) and RF39 (FDR-adjusted P = 0.042) etc., were decreased along with the reduction of LysoPC (18:1(9Z)) (FDR-adjusted P = 1.03 × 10− 3), LysoPC (16:0) (FDR-adjusted P = 0.0108), LysoPC (18:2(9Z, 12Z)) (FDR-adjusted P = 1.65 × 10− 3) and 8-Methylnonenoate etc. Conclusion The results indicated the supplementation of inulin in dietary can increase the relative abundance of commensal microbiota and SCFAs-producing bacteria, meanwhile, upregulate amino acids (AAs) metabolism and downregulate lipid metabolism in rumen of dairy cows, which might further improve lactation performance and the level of serum lipids.