Effects of dietary supplementation of inulin on rumen fermentation and bacterial microbiota, inflammatory response and growth performance in finishing beef steers fed high or low-concentrate diet

Abstract The objective of this study was to evaluate the effects of dietary inulin supplementation on rumen fermentation and bacterial microbiota, inflammatory response, and growth performance in finishing beef steers fed high or low-concentrate diet. Twenty-four Simmental × Luxi crossbred steers were used under a 2 × 2 treatment with 2 diet types and 2 inulin levels. The 2 diet types consisted of a low-concentrate diet (LCD; concentrate:roughage = 40:60) and a high-concentrate diet (HCD; concentrate:roughage = 60:40) and inulin was supplemented into the diets at 0 or 2% (wt/wt). The trial lasted for 42 days. Rumen fluid and plasma samples were collected at the end of the animal trial. Rumen fluid samples were analyzed for pH, short-chain fatty acids, endotoxin (lipopolysaccharide, LPS), and bacterial microbiota. Illumina Miseq sequencing of the 16S rRNA gene was applied to investigate ruminal bacterial microbiota. Plasma samples were analyzed for concentrations of pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor alpha as well as acute phase proteins including LPS-binding protein, haptoglobin, serum amyloid A, and C-reactive protein. Results showed that the high dietary concentrate level shifted the ruminal fermentation pattern from acetate towards propionate, butyrate and valerate, and improved growth performance. However, the high dietary concentrate level promoted ruminal pH reduction and LPS release, decreased bacterial diversity and richness, modified bacterial composition, and increased systemic inflammatory response. Inulin supplementation into the LCD increased ruminal concentrations of propionate, butyrate and iso-butyrate, and improved growth performance. Inulin supplementation into the HCD increased bacterial alpha indices (1628 vs. 1364, 1574 vs. 1329, and 0.985 vs. 0.975 for ACE, Chao1, and Simpson indices, respectively) and operational taxonomic units (1243 vs. 1080), increased Bacteroidetes to Firmicutes ratio (0.84 vs. 0.59), and enhanced final body weight and feed utilization. In conclusion, dietary supplementation with inulin, regardless of the dietary concentrate levels, improved growth performance of finishing beef steers probably through either altering the fermentation pattern or improving ruminal bacterial microbiota, depending on the diet type. Nonetheless, inulin supplementation did not suppress inflammatory response resulting from feeding high-concentrate diet in beef steers.