PSV-18 High dietary starch and erratic feed management impact ruminal and colonic health and pathogenic bacteria prevalence and concentration in the gastrointestinal tract and liver of feedlot steers.

Abstract Investigating the relationships between feedlot management practices, gastrointestinal health, and bacterial pathogen load is crucial for understanding liver abscess development. This study evaluated the effects of dietary starch concentration and feed management regimen on gastrointestinal health and the prevalence of pathogenic bacteria linked to liver abscess formation. Crossbred beef steers (n = 720; initial body weight = 407 ± 4.53 kg) were assigned to receive 1 of 4 treatments in a randomized complete block design. Treatments were a 2 × 2 factorial arrangement of feedlot finishing diets with high starch and low roughage concentrations (HOT), or low starch and higher roughage concentrations (CON) fed to steers with consistent (REG) or erratic feed management, where steers received randomized variations in feed quantity and delivery time (ERR). At harvest, the rumen of each steer was evacuated, rinsed, and evaluated for papillae damage, scars, and lesions. Three steers per pen (n = 144) were selected as a subset for tissue collection, where 2 samples from the rumen and colon were collected from each animal. One sample was used to evaluate papillae morphology, rumen epithelial thickness, and colonic crypt depth and width. The second set of samples were used to determine the prevalence and concentration of pathogenic bacteria involved in liver abscess development. When a steer in the subset had a liver abscess, the intact abscess was also collected for bacteriological analysis. No interactions (P ≥ 0.11) between diet and management were observed for any of the variables evaluated. However, steers fed HOT had a greater (P < 0.01) proportion of minor ruminal damage, less (P < 0.01) rumen scarring, greater epithelial thickness (P ≤ 0.05), and shorter colonic crypt lengths (P = 0.03). Steers consuming HOT had greater prevalence of Fusobacterium (F.) subsp. funduliforme in liver tissue (P = 0.03) and Trueperella pyogenes in ruminal tissue (P < 0.01), and tended to have greater prevalence F. subsp. necrophorum in ruminal tissue (P = 0.09) compared to CON. Concentrations of F. subsp. funduliforme and F. subsp. necrophorum were greater (P ≤ 0.04) in ruminal tissue of HOT. Feed management did not affect (P ≥ 0.11) ruminal or colonic health, but cattle managed with ERR tended to have greater (P = 0.07) prevalence of F. subsp. necrophorum in ruminal tissue and had greater (P = 0.01) concentrations of F. subsp. funduliforme in the colon tissue. Increased inclusion of readily fermentable starch and reduced roughage in finishing diets exposes steers to ruminal and colonic damage and increases concentrations of pathogenic bacteria within the rumen, whereas prevalence of F. subsp. necrophorum in colonic tissues suggest the colon serves as a source of pathogens contributing to liver abscess formation.