SERUM NEUTRALIZING ANTIBODIES AGAINST FUSOBACTERIUM-NECROPHORUM LEUKOTOXIN IN CATTLE WITH EXPERIMENTALLY-INDUCED OR NATURALLY DEVELOPED HEPATIC-ABSCESSES

The relationship, between serum-neutralizing antibody against Fusobact erium necrophorum leukotoxin and hepatic abscesses was investigated in cattle fed diets supplemented with or without tylosin. Sixteen cattle (eight each in tylosin and in control groups) were inoculated intrapo rtally with F. necrophorum. Ultrasonographic scanning showed that all control animals developed hepatic abscesses after inoculation. In the tylosin group, two animals were free of abscess by d 7 and one was fre e by d 14. Leukotoxin-neutralizing antibody titers were low on d 0, bu t increased (P <.05) markedly after intraportal inoculation in both gr oups. In a second study, blood was collected at the time of slaughter from 141 feedlot cattle (36 fed diets with tylosin and 105 fed diets w ithout tylosin), and livers were examined for presence or severity of hepatic abscesses at slaughter. The incidences of hepatic abscesses we re 32% in the control group and 6% in the tylosin group. Antibody was detected in all animals; however, antibody titers were greater (P <.05 ) in cattle with abscessed liver than those without, and greater (P < .01) in the nontylosin than in the tylosin group. Abscess score and an tibody titer were correlated (r .34; P <.0001). We conclude that F. ne crophorum leukotoxin is highly antigenic and that anti-leukotoxin anti body titer is related to the severity of hepatic abscesses.