Evaluation of gastrointestinal and fecal microbial communities as markers of liver abscess risk in beef feedlot cattle.

Liver abscesses (LAs) are a prevalent and costly issue in the beef industry. Microbial translocation from the gastrointestinal tract is believed to be the underlying cause of LAs. However, little is understood about the factors that permit the passage of bacteria into the portal bloodstream, or where in the gastrointestinal tract this translocation is likely to occur. This study used 16S rRNA gene sequencing to characterize the microbial community composition of the rumen, small intestine, large intestine, and feces of steers with edible and abscessed livers of varying severity. The small intestine of steers with severe LAs had increased (P = 0.02) richness and evenness compared to cattle with edible livers. However, there were no differences in the alpha diversity among samples collected at other locations (P ≥ 0.08). Small intestine samples also had a reduced (P < 0.01) Firmicutes to Bacteroidota ratio for cattle with LAs compared to those with edible livers. Prevotellaceae and Synergistaceae family abundance differed in the small intestine of cattle with LAs. Differences in community composition were not identified in fecal, colon, or rumen samples in association with LA occurrence, and there were no differences related to bacteria that have been traditionally considered LA pathogens (e.g. Fusobacteria or Trueperella spp.). These findings suggest that the microbial communities of the small intestine may have an important influence on LA occurrence. However, differences in microbial communities were not identified in rumen and fecal samples that might be used in predicting LA occurrence. Although sampling techniques during the feeding period are still limited, advances in this area would greatly benefit LA research.