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Increasing condensed corn distillers solubles alters the rumen microbiome of beef cattle
Five ruminally-fistulated steers were used in a 5 × 5 Latin square design to determine the effects of increasing dietary fat from corn distillers solubles (CDS) on the rumen microbiome. Treatments included a corn-based control (CON), and four levels of CDS (0, 10, 19, and 27%) in a coproduct-based (corn gluten feed and soybean hulls) diet. Fat concentrations were formulated to 3, 5, 7, and 9%, respectively, for diets containing CDS, and all steers were fed to ad libitum intake once daily. After 18 d of adaptation to the diet, ruminal samples were collected 3 h post-feeding and separated into solid and liquid fractions. Bacterial DNA was extracted from the solid fraction after physical homogenization. Real-time quantitative PCR was used to determine dietary effects on the relative abundance of culturable bacterial species. Orthogonal contrasts were used to compare diets formulated to similar fat concentrations (CON and 10% CDS), determine linear, quadratic, and cubic effects of CDS inclusion, and compare CON with all CDS treatments. Of the evaluated species, Selenomonas ruminantium was the most prevalent at 0.5 to 1.9% relative abundance. Moreover, Selenomonas ruminantium increased with greater CDS inclusion (P < 0.001). Anaerovibrio lipolytica was affected by treatment (P < 0.001); steers fed 0% CDS had eight-fold greater relative abundance than any other treatment. A quadratic effect was observed for Butyrivibrio proteoclasticus with the greatest relative abundance at 0 and 27% CDS and the lowest at 19% CDS. Butyrivibrio proteoclasticus was also greater in steers fed 10% CDS compared with CON. Eubacterium ruminantium was not affected by treatment but was the second most abundant species evaluated (0.03 - 0.1%). Fibrobacter succinogenes was affected by treatment (P = 0.005) with a marked decrease for steers fed 19 and 27% CDS, yet relative abundance remained similar for steers fed CON and 10% CDS. Prevotella bryantii had a cubic response (P = 0.005) to CDS inclusion with the greatest relative abundance for steers fed 10% CDS followed by the lowest abundance for steers fed 19% CDS. Megasphaera elsdenii was affected by treatment (P < 0.001); the lowest relative abundance was observed for steers fed CON compared with CDS diets (P < 0.001) and the greatest relative abundance was observed for steers fed 19% CDS. Results suggest the rumen microbiome is impacted by substantial changes in dietary CDS.
Keywords: microbiome, distillers solubles, dietary fat