The aims of the present study were to investigate the antibody response of cows from an outbreak region to vaccination with a bivalent botulinum toxoid (Type C and D) on three occasions and to investigate the antibody response to vaccination with the botulinum toxoid in the presence of anti-BoNT antibodies. Twenty-two cows from an outbreak region and 10 cows from a farm without a history of botulism were used in this study. Blood samples were collected before each vaccination and three weeks after the third vaccination (days 0, 21, 42 and 63). The level of anti-BoNT/C antibodies steadily increased after each vaccination (0.471±0.04, 0.566±0.03 and 0.663±0.04, respectively); however, the levels of anti-BoNT/D antibodies were not significantly different after the second and third vaccinations (0.377±0.03, 0.493±0.03 and 0.465±0.03, respectively). Post vaccination antibody responses of animals found positive and negative for anti-BoNT antibodies at the beginning of the study were similar. The results of the present study indicated that vaccination of cattle with botulinum toxoid on three occasions is recommended, particularly in outbreaks that are suspected to be caused by BoNT/C and that presence of naturally acquired antibodies against BoNT did not interfere with post vaccination immune response.

Key words: Antibody, BoNT, Botulism, ELISA, Vaccination