Rumen bacterial species associate with residual feed intake in beef cattle

Abstract Text:

Residual feed intake (RFI) describes an animal’s feed conversion efficiency independent of phenotypic performance. The objective of this study was to quantify differences in ruminal bacteria between the most efficient animals and the most inefficient animals, and any interaction with rumen sample fraction. One-hundred and fifty Red Angus cattle were allocated to three groups according to sex and herd origin. Animals were fed in confinement for at least 78 d to determine the RFI category for each. Within each contemporary group, the two most efficient (n = 6) and least efficient animals (n = 6) were selected. Rumen solids and fluid were collected immediately after slaughter. Bacterial DNA extraction from the solid fraction included mechanical homogenization followed by enzymatic and bead beating lysis for all samples. Real-time quantitative PCR was used to examine the relative abundance of specific ruminal bacteria compared with the geometric mean of two universal 16S rRNA primers. Data were analyzed using the MIXED procedure of SAS 9.3. Fixed effects in the model included RFI category, rumen fraction, RFI × fraction, and sex. Individual animal was the experimental unit and incorporated into the statistical model as a random effect nested within group. Of the nine species evaluated, Succinivibrio dextrinosolvens was the most-abundant averaging 1.8% of 16S rRNA copy number. Results indicated most efficient cattle had a 6-fold decrease (P = 0.04) in relative abundance of Succinivibrio dextrinosolvens while also having a 4-fold reduction (P = 0.02) in Anaerovibrio lipolytica. Although most efficient cattle tended (P = 0.09) to have greater relative abundance of Eubacterium ruminantium, a tendency (P = 0.10) for an RFI × fraction effect indicated the greatest differences were between the solid fraction of most efficient and least efficient cattle. Fraction effects were observed for Butyrivibrio proteoclasticus (P < 0.001) and Selenomonas ruminantium (P < 0.001) as each were increased within the solid fraction compared with the liquid. An RFI × fraction effect (P = 0.01) also was observed for Fibrobacter succinogenes with a greater relative abundance in the liquid compared with the solid fraction for least efficient cattle. No effect of RFI or fraction was observed for Megasphaera elsdenii or Prevotella bryantii. These findings indicate large differences in RFI phenotypes in beef cattle are associated with bacterial species in the rumen, and they may have a role in conferring feed efficiency.

Keywords:

residual feed efficiency, rumen, bacteria