Histopathology of ileal and liver tissues from Holstein steers in an experimental liver abscess challenge model

Introduction Our objective was to investigate the effects of diet and intraruminal inoculations with Fusobacterium necrophorum , Salmonella enterica , and Trueperella pyogenes on the microstructure of ileal and liver tissues in Holstein steers experimentally challenged to induce liver abscesses (LA). Methods Ileal epithelium and liver tissues were collected from Holstein steers ( n = 80) across two separate experiments for histopathological analysis. Steers in Exp. 1 were assigned to one of three treatments: 1) low-starch control diet (CON1; n = 13); 2) high-starch acidotic diet (AD1; n = 13); or 3) high-starch acidotic diet plus intraruminal inoculation with F. necrophorum subsp. necrophorum , S. enterica serotype Lubbock, and T. pyogenes (1 × 10 9 CFU/mL in 100 mL; ADB; n = 14). In Exp. 2, steers were assigned to one of four treatments: 1) low-starch control diet (CON2; n = 10); 2) high-starch acidotic diet (AD2; n = 10); 3) high-starch acidotic diet with intraruminal inoculation with F. necrophorum subsp. necrophorum (8.81 × 10 8 CFU/mL; ADF; n = 10); or 4) high-starch acidotic diet with intraruminal inoculation with F. necrophorum subsp. necrophorum (8.81 × 10 8 CFU/mL) combined with S. enterica subsp. Lubbock (1.52 × 10 9 CFU/mL; ADFS; n = 10). Results In Exp. 1 and 2, steers on high-starch acidotic diets (AD1, AD2) or inoculated with bacteria (ADB, ADF, and ADFS) had shorter ileal villi height and greater crypt depth compared with low-starch controls (CON1 and CON2; P < 0.01). Inflammatory cell counts were consistently elevated in acidotic and inoculated treatments, particularly ADFS ( P ≤ 0.05). Ileal villi height was shorter in Exp. 2, and crypt depth was reduced in steers with and without LA between experiments ( P ≤ 0.10). In Exp. 2, liver tissue damage was greatest for ADFS steers and least for CON2 steers ( P ≤ 0.03). Liver lymphocyte foci area was lower ( P = 0.02) and neutrophil score tended to be lower ( P = 0.08) in steers with LA. Discussion When acidotic cycles were coupled with bacterial inoculations, steers exhibited greater intestinal damage, immune cell infiltration, and liver pathology. Overall, these findings underscore that diet and pathogen exposure can synergistically modulate tissue damage and infection risk.