Development of an experimental model to induce liver abscesses in steers using an acidotic diet challenge and intraruminal bacterial inoculation

Authors: MCDANIEL, ZACH - Texas Tech University; HALES, KRISTIN - Texas Tech University; SALIH, HARITH - Kansas State University; DETERS, ALYSSA - Kansas State University; SHI, XIAORONG - Kansas State University; NAGARAJA, T - Kansas State University; LAWRENCE, TY - West Texas A & M University; AMACHAWADI, RAGHAVENDRA - Kansas State University; TENNANT, TRAVIS - West Texas A & M University; Carroll, Jeffery - Jeff Carroll; Sanchez, Nicole; GALYEAN, MICHAEL - Texas Tech University; SMOCK, TAYLOR - Texas Tech University; BALLOU, MICHAEL - Texas Tech University; MACHADO, VINICIUS - Texas Tech University; DAVIS, EMILY - Texas Tech University; Broadway, Paul

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2023
Publication Date: 3/6/2024
Citation: McDaniel, Z.S., Hales, K.E., Salih, H., Deters, A., Shi, X., Nagaraja, T.G., Lawrence, T.E., Amachawadi, R.G., Tennant, T.T., Carroll, J.A., Sanchez, N.C., Galyean, M.L., Smock, T.M., Ballou, M.A., Machado, V.S., Davis, E., Broadway, P.R. 2024. Development of an experimental model to induce liver abscesses in steers using an acidotic diet challenge and intraruminal bacterial inoculation. Journal of Animal Science. 102(3). https://doi.org/10.1093/jas/skad281.082.
DOI: https://doi.org/10.1093/jas/skad281.082

Interpretive Summary: Liver abscesses in feedlot cattle can result in decreased feed intake, average daily gain, gain efficiency, and hot carcass weight. Presence of liver abscesses in cattle after harvesting increases liver condemnations, carcass trimming, and decrease quality grade with an estimated economic cost to packers of $41.6 million per year. Models that induce and describe the origins of liver abscess are difficult to develop. Development of a repeatable model to study the origin of liver abscesses would be valuable to the entire beef industry. Scientists in Lubbock, Texas and university partners evaluated diet changes followed by oral dosing with bacteria common to liver abscesses in order to develop a model to elucidate the origin of liver abscesses. Data from this study reports that feeding an acidotic diet in combination with bacteria common to liver abscesses is a viable model to induce liver abscesses. Abscesses formed within 20 days in 50% of the inoculated animals. Interestingly, calves fed an acidotic diet but not inoculated did not form liver abscesses. Development of this non-invasive model is an important step to further understand liver abscess formation and explore preventative measures. These data will be of interest to researchers, producers, packers, and animal health professionals.

Technical Abstract: Holstein steers (n = 40; initial BW = 84.9 ± 7.1 kg) were used to study the genesis of liver abscesses (LA) using an acidotic diet challenge with or without intraruminal bacterial inoculation. Steers were housed in individual pens inside a climate-controlled barn for 50 d and randomly assigned to 1 of 3 treatments: 1) control diet (CON); 2) acidotic diet (AD); or 3) acidotic diet plus intraruminal inoculation with Fusobacterium necrophorum subsp. necrophorum, Trueperella pyogenes, and Salmonella enterica serovar Lubbock, previously isolated from liver abscesses (~1 × 10 exp 9 colony forming units [CFU]/mL of each bacterial species; ADB). Four acidotic cycles for AD and ADB where steers were fed the acidotic diet for 3 d followed by 2 d of the CON diet. On d 23, ADB steers were intraruminally inoculated with the bacterial mixture. After euthanasia, steers were necropsied to record gross pathology of livers, lungs, rumens, and colons. Continuous data were analyzed in PROC GLIMMIX of SAS as repeated measures over time with individual steer as the experimental unit. The PROC GLIMMIX procedure was also used for necropsy scores to determine the difference in percentage prevalence among treatments. For all analyses, the model included treatment, time, and the treatment × time interaction. Ruminal pH decreased in AD and ADB steers during each acidotic diet cycle (P = 0.05). Liver abscess prevalence was 42.9% (6 of 14) in ADB vs. 0% in AD or CON treatments (P < 0.01). Ruminal damage was 51.1% greater in ADB than in AD (P = 0.04). Culture techniques from the LA found 100% of the abscesses contained F. necrophorum subsp. necrophorum, 0% contained T. pyogenes, 50% contained Salmonella, and 50% contained a combination of F. necrophorum subsp. necrophorum and Salmonella. The F. necrophorum subsp. necrophorum was clonally identical to the strain used for the bacterial inoculation based on phylogenetic analysis of the whole genome. This experimental model successfully induced rumenitis and LA in Holstein steers and confirms the central dogma in the pathogenesis that acidosis and rumenitis lead to the entry of F. necrophorum into the liver to cause abscesses. Our findings suggest that an acidotic diet, in conjunction with intraruminal bacterial inoculation, is a viable model to induce LA. Further research is needed to determine the repeatability of this model, and a major application of the model will be in evaluations of novel interventions to prevent LA.