Effects of neutral detergent fiber concentration in dietary roughage and bulk density of steam-flaked corn on the prevalence and concentration of Fusobacterium necrophorum and Fusobacterium varium in the ruminal contents of finishing beef steers*

Objective

We assessed the effects of NDF concentra- tion of dietary roughage and bulk density of steam-flaked corn on the prevalence and concentrations of Fusobacte- rium necrophorum ssp. necrophorum, F. necrophorum ssp. funduliforme, and Fusobacterium varium in the ruminal contents of finishing beef steers.

Materials and Methods

Crossbred beef steers (n = 104; initial BW = 417 ± 8.9 kg) were blocked by BW, as- signed randomly to treatments, and fed for 118 d. Treat- ments were arranged as a 2 × 3 factorial with 5 pens per simple-effect treatment and consisted of 3 NDF concentra- tions from alfalfa hay (3%, 4.5%, or 6%) and 309 g/L (24 lb/bu) or 412 g/L (32 lb/bu) steam-flaked corn (SFC; 69% or 33% starch availability, respectively). Ruminal content samples collected at the start of the finishing period (d 0) and the day before slaughter (d 118) were analyzed by quantitative PCR assay to determine the prevalence and concentrations of F. necrophorum and F. varium. Pen was the experimental unit for dietary treatment analyses. In- dividual animal was the experimental unit for analyses of liver abscess (LA) prevalence. The PROC GLIMMIX and MIXED procedures of SAS 9.4 were used to determine the effects of dietary treatments and LA prevalence on Fuso- bacterium populations in ruminal contents.

Results and Discussion

Liver abscess prevalence was greater in steers fed 3% roughage NDF from alfalfa hay compared with 4.5% and 6%. As bulk density increased from 309 to 412 g/L, LA prevalence tended to decrease 11.1 percentage points. Roughage NDF and bulk density of SFC did not affect F. necrophorum ssp. necrophorum or F. necrophorum ssp. funduliforme prevalence or concen- tration in ruminal contents. Fusobacterium varium con- centrations tended to be greater in steers fed 3.0% and 4.5% roughage NDF than in those fed 6% roughage NDF. Prevalence and concentration of F. necrophorum and F. varium did not differ between steers with or without LA regardless of experimental diet.

Implications and Applications

Increasing roughage NDF from alfalfa hay and SFC bulk density decreased LA prevalence; however, these dietary changes did not signifi- cantly alter Fusobacterium prevalence or concentrations in ruminal contents. The lack of clear associations between Fusobacterium populations and dietary strategies or LA prevalence suggests a need to refine our understanding of microbial and dietary contributions to LA etiology. Future research should explore how interactions between feed in- take patterns, dietary ingredients, and microbial competi- tion contribute to LA risk.