Short communication: evaluation of an endotoxin challenge and intraruminal bacterial inoculation model to induce liver abscesses in Holstein steers

Abstract

Holstein steers (n = 40; initial body weight [BW] = 96.0 ± 10.5 kg) were individually housed in a climate-controlled barn to evaluate potential models for the genesis of liver abscesses (LA). In this 2 × 2 factorial, steers were balanced by BW and randomly assigned to one of two treatments: 1) intravenous saline injection followed by intraruminal bacterial inoculation with Fusobacterium necrophorum subsp. necrophorum (1 × 109 colony forming unit [CFU]/mL) and Salmonella enterica serovar Lubbock (1 × 106 CFU/mL; CON; n = 20 steers); or 2) intravenous injection with 0.25 µg/kg BW of lipopolysaccharide (LPS; Escherichia coli O111:B4) followed by intraruminal bacterial inoculation of F. necrophorum subsp. necrophorum (1 × 109 CFU/mL) and S. enterica serovar Lubbock (1 × 106 CFU/mL; LBI; n = 20 steers) and 1 of 2 harvest dates (3 or 10 d post LPS infusion). Body weights were recorded on days -4, -1, 3, and 10, and blood was collected for hematology on days -4, 3, and 10, relative to LPS infusion on day 0. Intraruminal bacterial inoculation occurred on day 1. Steers from each treatment group were harvested at two different time points on day 3 or 10 to perform gross pathological examination of the lung, rumen, liver, LA (if present), and colon. Feed disappearance was less for LBI than CON (P < 0.01); however, BW did not differ (P = 0.33) between treatments. Neither treatment nor time differed for hematology (P ≥ 0.13), and no gross pathological differences were noted in the lung, liver, LA, or colon (P ≥ 0.25). A treatment × harvest date interaction was noted for ruminal pathology in which LBI had an increased percentage of abnormal rumen scores on day 3 (P < 0.01). These results suggest that an LPS challenge in combination with intraruminal bacterial inoculation of pathogens commonly isolated from LA was not sufficient to induce LA in steers within 3 or 10 d (P = 0.95) when compared to CON. Further evaluation is needed to produce a viable model to investigate the genesis and prevention of LA in cattle.

Keywords: bacterial inoculation; cattle; liver abscess formation.

Figure 1.

Daily feed disappearance over sampling days of Holstein steers given either an intravenous injection of saline solution (CON) or lipopolysaccharide (0.25 µg/kg BW) and intraruminally inoculated with a mixture of Fusobacterium necrophorum subsp. necrophorum (1 × 10⁹ CFU/100 mL), and Salmonella enterica serovar Lubbock (1 × 10⁶ CFU/100 mL; LBI) to induce liver abscesses. Feed disappearance was recorded the same time daily (0800 hours) for individual steers. The LPS challenge occurred on day 0, where treatment LBI was intravenously dosed with 0.25 µg/kg (Escherichia coli O111:B4). Ruminal bacterial inoculation of Fusobacterium necrophorum subsp. necrophorum and Salmonella enterica serovar Lubbock occurred on day 1. Standard error of least squares mean (n = 10 to 20 steers/mean), error bar denotes SEM. Treatment (P < 0.01), time (P < 0.01), and treatment × time (P = 0.26).