FAILURE OF A SINGLE DOSE OF BRUCELLA ABORTUS STRAIN 19 VACCINE TO PROTECT CATTLE WHEN GIVEN EARLY IN CALFHOOD

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Abstract
SUMMARY Groups of heifer calves were vaccinated subcutaneously with the standard dose of strain 19 at the age of 3 to 5 weeks or 5 months. Twelve months after primary vaccination a group of the younger vaccinates were revaccinated with a small dose of strain 19 via the conjunctival sac. The effectiveness of vaccination was assessed by challenge with virulent B. abortus after 5 to 6 months of pregnancy. Animals vaccinated at 3 to 5 weeks, but given no intraconjunctival boost, were not effectively protected, but the group receiving the boost were at least as resistant as those which received the subcutaneous dose at 5 months. The intraconjunctival boost caused only slight and transient serological responses in a few animals.