VACCINATION OF HEIFERS WITH A REDUCED DOSE OF BRUCELLA ABORTUS STRAIN 19 VACCINE BEFORE FIRST MATING

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Abstract
Ten Jersey heifers aged 14-23 mo. were vaccinated with 2.25 .times. 108 cells of living B. abortus strain 19 vaccine. They and 10 similar non-vaccinated heifers were subsequently mated and when about 6 mo. pregnant were challenged by the conjunctival application of a virulent culture of B. abortus. The serological response to vaccination was much less than is usually seen following vaccination with the normal dose of strain 19, especially when the indirect hemolysis test was used. A persistent vaccinal reaction was observed in 1 heifer. Significant resistance to infection was demonstrated which was greater than that previously observed in calfhood vaccinates given the full dose, but less than that shown by cows given the smaller dose in early pregnancy. The effectiveness of strain 19 vaccination appears to be related to the age of the animal at vaccination.