['To determine the efficacy of leukotoxin-based Fusobacterium necrophorum vaccines and dietary tylosin in providing protection against experimentally induced hepatic abscesses in steers.', '30 steers assigned randomly to 6 treatment groups of 5 steers each: 1, phosphate-buffered saline solution (PBSS; control); 2, PBSS control, fed tylosin (100 mg/steer) daily; 3, inactivated whole-cell culture with oil emulsion adjuvant; 4, culture supernatant (crude toxoid) with oil emulsion adjuvant; 5, semipurified leukotoxoid with oil emulsion adjuvant; and 6, semipurified leukotoxoid with saponin adjuvant.', 'Steers were inoculated SC with emulsified antigen or PBSS on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum antileukotoxin antibody titer. On day 42, all steers were challenge exposed intraportally with F necrophorum culture. Three weeks later (day 63), steers were euthanatized and necropsied to examine liver and assess protection.', 'Antileukotoxin antibody titers of all vaccinated groups markedly increased from baseline values, and mean titers of vaccinated groups were higher than those of the control and tylosin-treated groups. Steers vaccinated with culture supernatant with oil emulsion adjuvant or semipurified leukotoxoid with saponin adjuvant had the highest mean antibody titers. All 5 steers in the control group developed liver abscesses. Tylosin feeding did not protect steers challenge exposed with F necrophorum intraportally.'] Does serum neutralizing antibody response and protection against experimentally induced liver abscesses in steer vaccinated with Fusobacterium necrophorum?