Validation of an experimental model to induce liver abscesses in Holstein steers using an acidotic diet challenge and intraruminal bacterial inoculation*†

Objective Our objectives were to develop and evaluate a model to induce liver abscesses (LA) in cattle and assess roles of Fusobacterium and Salmonella on LA formation and severity. Materials and Methods Holstein steers (n = 40; initial BW = 110 ± 12.0 kg) were assigned randomly to treatments (n = 10 per treatment): (1) control diet (CON); (2) acidotic diet (AD); (3) AD plus inoculation of Fusobacterium necrophorum ssp. necrophorum (8.81 × 1010 cfu/steer; ADFn); or (4) AD and intraruminal inoculation of F. necrophorum (8.81 × 1010 cfu/steer) and Salmonella enterica Lubbock (1.52 × 1011 cfu/steer; ADFS). On d 0, steers were subjected to 4 acidotic cycles where they were fed the acidotic diet for 3 d and then the control diet for 2 d. Intraruminal bacterial inoculation was on d 20. From d 21, AD, ADFn, and ADFS steers remained on the acidotic diet until d 38. Euthanasia occurred on d 38, and gross pathology of the lung, rumen, liver, and colon were recorded. Results and Discussion Liver abscess prevalence was 40% in ADFn and 50% in ADFS versus 0% in CON and AD. No pathological differences were noted in lung nor colon among treatments; however, ruminal damage was more severe in ADFn and ADFS than in CON and AD steers. Implications and Applications Acidotic diet alone caused mild ruminal acidosis but no LA. Acidotic diet with intraruminal bacterial inoculation increased rumenitis severity and resulted in LA, thus validating the nutritional model to induce LA. Therefore, acidotic diet with intraruminal bacterial inoculation is a viable model to study the formation of LA.