Revaccination with a reduced dose of Brucella abortus strain 19 vaccine of breeding cows in the Pampas region of Argentina

In a breeding herd previously infected with brucellosis, 203 cows of various crossbreeds were inoculated subcutaneously with a dose of 3.1 x 10 colony-forming units (CFU) of Brucella abortus strain 19. They had been vaccinated as calves with the standard dose of 60 x 10 CFU of this vaccine strain, and had become negative to the slow tube agglutination test (SAT) at the moment of revaccination. Another 137 cows in the same herd were not revaccinated in order to serve as controls for the natural course of infection.