Isolation of Fusobacterium Necrophorum, Trueperella Pyogenes, and Salmonella Enterica from Ruminal, Ileal, and Colonic Epithelial Tissues of Finishing Beef Steers Receiving Different Levels of Dietary Roughage with and without Tylosin

To improve our ability to prevent liver abscesses in finishing beef steers, we must evaluate the possibility of pathogens originating from the hind gut as well as the rumen. We hypothesized that pathogens promoting liver abscess formation are located throughout the gut. Furthermore, the increased dietary roughage levels could improve gut integrity overtime. This experiment was conducted to isolate specific pathogens within the ruminal, ileal, and colonic epithelial tissues. Treatment diets were steam-flaked corn-based with 5 or 15% corn stalk inclusion (DM basis) with (5T and 15T) or without (5NT and 15NT) tylosin. Two hundred sixty-four crossbred beef steers (BW = 257 ± 18 kg) were used in a randomized complete block design with 8 hd/pen (8 pens/treatment). Half of the pens for each treatment were designated for serial slaughter while the other half remained on feed the entire experiment for performance evaluation. Steers were fed each day at 0730 h for an average of 220 d (heavy block = 205 d, light block = 234 d). At trial initiation, 8 steers were slaughtered for initial tissue sampling and 1 pen/treatment was slaughtered every 56 d thereafter. During serial slaughter, a dorsal and ventral sample of the rumen was taken for histopathological evaluation along with ruminal, ileal, and colonic tissue for bacterial isolation. Performance data were analyzed using the MIXED procedure of SAS and pen was the experimental unit. Bacterial isolation data were analyzed using the GLMMIX procedure of SAS and animal was the experimental unit. Means were separated using LSMEANS with PDIFF option. There were no differences between treatments for final BW (P = 0.93) and feed conversion (P = 0.17). The 15NT treatment had the greatest (P = 0.04) ADG and 5NT the lowest, with 15T and 5T intermediate. None of the cattle, except one, had abscessed livers. There were no differences in the prevalence of Fusobacterium necrophorum, Trueperella pyogenes, and Salmonella enterica in ruminal, ileal, and colonic epithelial tissues (P ≥ 0.35). However, this experiment was the first to isolate F. necrophorum in ileal and colonic epithelial tissues of finishing beef steers, which suggests that post-ruminal gut tissue could be a source of F. necrophorum. With limited efficacy of tylosin in the hind gut, further research is warranted to explore post-ruminal acidosis and its effects on gut epithelial integrity, pathogen prevalence, and liver abscess formation.