Serum antibody titres were followed for a period of two years in 99 beef and 29 dairy cows which had been vaccinated as adults with B. abortus strain 19. Agglutination titres remained above diagnostic levels throughout but complement fixation, mercaptoethanol agglutination and rivanol agglutination titres generally returned to negative levels within 6 months. Coombs tests and agglutination at 56° proved to be of limited value for recognising antibody titres caused by vaccination.
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