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

This study evaluated the main and interactive effects of dietary starch concentration (49.1% [control] or 64.4% [high starch]) and feeding management regimen (regular [REG] or erratic [ERR]) on prevalence of Fusobacterium necrophorum subsp. necrophorum, F. necrophorum subsp. funduliforme, Trueperella pyogenes and Salmonella enterica in liver abscesses (LA) and ruminal and colonic tissues of finishing beef steers. Intact LA (n = 132) and sections of ruminal (n = 131) and colonic (n = 120) epithelial tissues were collected from steers at slaughter. Samples were cultured, before and after enrichment, to determine prevalence of four bacterial pathogens and quantitative PCR (qPCR) was used to determine prevalence and concentrations of the two subspecies of F. necrophorum. Subsp. necrophorum was the dominant pathogen in LA, whereas subsp. funduliforme was dominant in ruminal and colonic tissues by both culture and qPCR methods. Steers fed the high starch diet had greater prevalence (P = 0.01) of subsp. necrophorum, T. pyogenes, and S. enterica in LA compared to steers fed the control diet, indicating the potential impact of dietary starch on promoting bacterial translocation. Of the 132 LA analyzed, culture and qPCR identified 21.7% and 16.4% of LA, respectively, to have subsp. funduliforme, without the subsp. necrophorum, suggesting that subsp. funduliforme without subsp. necrophorum may have caused LA. Concentrations of F. necrophorum in LA were between 7.0 to 7.5 log10 CFU per g and were 2 to 3 log less in ruminal and colonic epithelial tissues and were not affected by the diet (P ≥ 0.08). The prevalence of S. enterica was greater (P < 0.01) in colonic (71.9%) than ruminal epithelial tissues (48.3%), suggesting that the colon may be the major source of the Salmonella in LA. A total of 8 serotypes were identified, and the majority (88.6%) belonged to Kentucky (27.2%), Montevideo (26.2%), Anatum (23.3%), and Lubbock (11.9%). Feeding management regimen had minimal effect, however, diet affected prevalence of the pathogens in LA but not ruminal and colonic epithelial tissues. The prevalence and concentrations of both subspecies of F. necrophorum in colonic epithelial tissue suggest the possibility of the colon being a source of LA pathogens. However, the prevalence and concentration of F. necrophorum in colonic epithelial tissues were much less than that of ruminal tissues, suggesting that the rumen may be the primary reservoir of F. necrophorum in LA.