Effects of corn stalk inclusion and tylosin on performance, rumination, ruminal papillae morphology, and gut pathogens associated with liver abscesses from finishing beef steers

To reduce prevalence of 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, and increased dietary roughage levels could improve gut integrity over time. Two hundred sixty-three crossbred beef steers (BW = 258 ± 29 kg) were used in a randomized complete block design with 7-8 hd/pen (8 pens/treatment) using a 2 × 2 factorial treatment structure. Steers received steam-flaked corn-based diets with 5 or 15% corn stalk (CS) inclusion (dry matter basis, DMB) and with (TYL) or without (NTYL) tylosin (7.9 g/T; DMB). Half of the pens in each treatment remained on feed for the entire experiment duration (Exp 1) whereas the remaining half were designated for serial slaughter (Exp 2). Steers were fed each day at 0700 h for an average of 220 d (heavy block = 175 d, light block = 233 d). For Exp 2, eight steers were slaughtered on d 0 to obtain initial tissue samples and thereafter one pen/treatment was slaughtered every 56 d. During serial slaughter, dorsal and ventral sac rumen tissue samples were collected for histopathological evaluation along with ruminal, ileal, and colonic tissues for bacterial isolation. Data were analyzed using mixed models; pen was the experimental unit for performance outcomes and individual animal was the experimental unit for bacterial isolation and histopathological data. No interaction (P ≥ 0.40) between tylosin and CS inclusion was detected for ADG or final BW. Interactions were detected for DMI and G:F; both outcomes were similar when tylosin was included in the diet, however both outcomes differed notably without tylosin. Perimeter and length of ventral rumen papillae decreased (P ≤ 0.01) as DOF increased. In contrast, dorsal rumen papillae perimeter and length increased through d112 and then decreased through d231. Corn stalk inclusion rate did not affect the incidence of bacterial species isolated from the ruminal (P = 0.38), ileal (P > 0.15), or colonic (P > 0.37) epithelial tissues. Cattle consuming the TYL diets tended to have decreased (P = 0.06) presence of ileal Fusobacterium necrophorum subsp. necorphorum and increased (P = 0.07) rates of ruminal Salmonella enterica compared to NTYL. Prolonged consumption of a finishing diet, regardless of CS or TYL inclusion, seemed to be the major source of change in rumen epithelial tissue morphology.