SERUM NEUTRALIZING ANTIBODY-RESPONSE AND PROTECTION AGAINST EXPERIMENTALLY-INDUCED LIVER-ABSCESSES IN STEERS VACCINATED WITH FUSOBACTERIUM-NECROPHORUM

Objective-To determine the efficacy of leukotoxin-based Fusobacterium necrophorum vaccines and dietary tylosin in providing protection again st experimentally induced hepatic abscesses in steers. Design-30 steer s assigned randomly to 6 treatment groups of 5 steers each: 1, phospha te-buffered saline solution (PBSS; control); 2, PBSS control, fed tylo sin (100 mg/steer) daily; 3, inactivated whole-cell culture with oil e mulsion adjuvant; 4, culture supernatant (crude toxoid) with oil emuls ion adjuvant; 5, semipurified leukotoxoid with oil emulsion adjuvant; and 6, semipurified leukotoxoid with saponin adjuvant. Procedure-Steer s were inoculated SC with emulsified antigen Or PBSS on days 0 and 21. Blood samples were collected at weekly intervals to monitor serum ant ileukotoxin antibody titer. On day 42, all steers were challenge expos ed intraportally with F necrophorum culture. Three weeks later (day 63 ), steers were euthanatized and necropsied to examine liver and assess protection. Results-Antileukotoxin antibody titers of all vaccinated groups markedly increased from baseline values, and mean titers of vac cinated groups were higher than those of the control and tylosin-treat ed groups. Steers vaccinated with culture supernatant with oil emulsio n adjuvant or semipurified leukotoxoid with saponin adjuvant had the h ighest mean antibody titers. All 5 steers in the control group develop ed liver abscesses. Tylosin feeding did not protect steers challenge e xposed with F necrophorum intraportally. Conclusions-Culture supernata nt was more protective than whole-cell culture or semipurified leukoto xin against experimentally induced hepatic abscesses. Partial purifica tion of leukotoxin appeared to reduce its protective immunity.