Effects of dietary starch concentration and feeding management regimen on bacterial pathogens in liver abscesses and ruminal and colonic epithelial tissues in feedlot steers

Lay Summary Feedlot cattle are fed high-grain diets and typically experience fluctuations in daily feed intake that may increase liver abscess prevalence. Liver abscesses result from bacterial infection, but the interaction between feedlot management practices and bacterial prevalence and concentrations in the liver and the gastrointestinal tract are poorly understood. This study was designed to evaluate the individual and interactive effects of dietary starch concentration (moderate or high) and feeding management regimen (regular or erratic) on the prevalence of bacterial pathogens in liver abscesses, ruminal, and colonic epithelial tissues of finishing beef steers. Culture-based and molecular methods were used to determine the prevalence of the four primary and secondary bacterial pathogens and concentrations of the primary bacterial pathogen implicated in liver abscesses. Feeding high concentrations of dietary starch increased the prevalence of pathogens in liver abscesses, but not ruminal or colonic epithelial tissues. However, the prevalence of liver abscess causing pathogens in colonic tissues indicated that the colon may also serve as a source of these pathogens, in addition to the rumen. Because the prevalence and concentrations of the primary bacterial pathogen in colonic epithelial tissues were much lower than ruminal epithelial tissues, the rumen may be the major source of pathogens that reach the liver.