Culture- and polymerase chain reaction–based prevalence of bacterial pathogens in liver abscesses and ruminal wall tissues of beef-on-dairy feedlot cattle fed finishing diets with no additives, tylosin, or antibiotic alternatives to control liver abscesses*

Abstract

Objective

Our objectives were to investigate the prevalence and concentrations of major bacterial pathogens associated with liver abscesses and ruminal epithelial tissues of beef-on-dairy heifers fed finishing diets containing no additives (negative control), tylosin, or a probiotic (yeast) and zeolite combination to control liver abscesses.

Materials and Methods

A total of 74 liver abscesses and 69 ruminal epithelial tissues, collected at slaughter, were subjected to culture-based methods to isolate 5 bacterial species, Fusobacterium necrophorum ssp. necrophorum, F. necrophorum ssp. funduliforme, Trueperella pyogenes, Salmonella enterica, and Escherichia coli, and to a quantitative PCR (qPCR) assay to determine prevalence and concentrations of the 2 F. necrophorum subspecies. Statistical analyses included Fisher’s exact test for prevalence and ANOVA for bacterial concentrations to compare the treatment groups.

Results and Discussion

Both culture method and qPCR assay indicated that the ssp. necrophorum was the dominant pathogen, and the prevalence tended to be greater in the negative control group than in the tylosin or yeast-plus-zeolite groups. The prevalence of ssp. funduliforme was not different between the treatment groups. Concentrations of both subspecies were in log 6 to 7 cfu/g and were not affected by treatment. The prevalence of T. pyogenes and S. enterica were low, but the prevalence of E. coli was high. A total of 5 liver abscesses were negative for both subspecies, suggesting that 6% of abscesses were caused by pathogens other than F. necrophorum. In ruminal tissues, the prevalence of ssp. funduliforme was greater than the ssp. necrophorum.

Implications and Applications

The combination of culture method and qPCR assay provided complementary assessment of the prevalence of the major pathogens in liver abscesses of beef-on-dairy cattle, which was similar to that of liver abscesses in cattle of beef breeds. This is the first study that used a qPCR assay to detect and quantify the 2 subspecies of F. necrophorum in liver abscesses.