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SUMMARY Three groups, each of 14 mature Jersey heifers, were vaccinated. They were mated about 2 months later and those that became pregnant were challenged at about 6.5 months of pregnancy by the conjunctival application of virulent Brucella abortus. Group 1 heifers received 2 doses of B. abortus 45/20 vaccine 2 months apart. Only 5 of the 14 heifers became pregnant, and of these 5 only one resisted challenge. Group 2 heifers received only one dose of 45/20 vaccine, 5 of the 10 challenged resisted infection. Group 3 heifers received 3 × 108 cfu of strain 19. Six of the 10 heifers challenged resisted infection. All of 5 non-vaccinated control cattle became infected. It appeared advantageous to give only one dose of 45/20 rather than 2 as presently recommended. A single dose of 45/20 vaccine induced resistance to virulent B. abortus approximately equal to that given by the reduced dose of strain 19. One dose of 45/20 vaccine stimulated transient serological positivity in 2 of 28 heifers whereas the reduced dose of strain 19 gave rise to persistent titres in 2 of 14 vaccinated heifers.

SUMMARY Lesions induced by inoculation of Brucella ovis into the epididymis were compared in rams previously vaccinated with B. ovis bacterin and unvaccinated rams. Inoculation of killed B. ovis did not produce significant lesions in either group whereas prior vaccination exacerbated epididymal lesions following inoculation of live B. ovis. Increased numbers of neutrophils, macrophages and lymphocytes were present in the interstitium and neutrophilic infiltration of the epididymal duct epithelium and intraepithelial cyst formation was more prominent. The inflammatory response surrounding extravasated spermatozoa was more severe in vaccinated rams but it was not determined if the response was directed at spermatozoa or intermixed brucellae, or both.

Bovine field serums from the Australian brucellosis eradication program were used to compare 2 enzyme linked immunosorbent assays (ELISA) with the complement fixation test (CFT) and Rose Bengal test (RBT). One ELISA used an anti-bovine IgG horseradish peroxidase conjugate (ELISA 1) and the other a monoclonal anti-bovine Ig alkaline phosphatase conjugate (ELISA 2). When compared with the CFT, the ELISA 2 like the ELISA 1 lacked specificity in B. abortus vaccinated herds but the ELISA 2 was more specific than the ELISA 1 in previously infected herds and equally as specific as the ELISA 1 in nonvaccinated Brucella free herds. In this study the ELISA 2 proved more sensitive than the CFT, RBT and ELISA 1 particularly in herds where B. abortus biotype 2 was present. The value of using the ELISA 2 in conjunction with the CFT in an eradication program is discussed.

SUMMARY A group of 4 cows was vaccinated with Brucella abortus strain 19, followed 8 weeks later by a single dose of B. abortus 45/20 vaccine. A similar group received 2 doses of B. abortus 45/20 vaccine 8 weeks apart. The antibody responses of the groups were compared by testing whole serums and separated IgM and IgG fractions by the Rose Bengal Plate (RBP) agglutination and the complement fixation tests (CFT) using rough and smooth B. abortus antigens. Animals that had received B. abortus strain 19 responded to the 45/20 vaccine with increased titres to the smooth antigen. These relevant antibodies were predominantly of the IgG class. Standard CFT and RBP test antibodies could be detected in IgM and IgG fractions after the primary inoculation with B. abortus strain 19 vaccine.

Data from 42,224 cattle from 694 herds collected during the brucellosis eradication campaign were used to examine the effects of calfhood strain 19 vaccination. The prevalence to infection in vaccinated herds was 1.8% compared with 9.1% in non-vaccinated herds (p less than 0.005). The mean titre in the former group was lower (p less than 0.001). Vaccinated herds required 3.3 herd tests to achieve a provisionally free status compared with 4.8 in non-vaccinated herds (0.001 less than p less than 0.005). Vaccination did not significantly reduce the number of herd test in herds with less than 100 breeding females. In tests after the initial herd test only 0.5% reactors were found in vaccinated herds compared with 6.9% in non-vaccinated herds (p less than 0.005). There were 0.9% false positive to the Rose Bengal plate test in non-vaccinated and 2.1% in vaccinated animals (p less than 0.005) in non-infected herds. In infected herds this percentage was 3.0% and 4.2% respectively by (p less than 0.05). In the non-infected herds there were 0.04% false positives to the complement fixation tests out of 10,506 non-vaccinated cattle tested and 0.2% out of 24,734 vaccinated cattle.

The immunoglobulin class specificity of non-agglutinating antibody produced following vaccination with Br. abortus 45/20 vaccine was determined using the antiglobulin test. In previously unvaccinated cattle it was found that most of the non-agglutinating antibody was associated with the IgG1 immunoglobulin class. In cattle sensitised to Brucella antigens by prior vaccination with Brucella abortus strain 19 the majority of antibody was also associated with the IgG1 immunoglobulin class, but a significant amount of IgG2 antibody was also present. The results indicate that the significance of levels of IgG2 antibody would be difficult to determine in cattle repeatedly exposed to Brucella antigens.

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.

Two groups, each of 9 Jersey cows, were vaccinated subcutaneously with reduced doses of Brucella abortus strain 19 vaccine (measured by the number of bacteria in the vaccine dose) early in their second pregnancy. Ten weeks later they were challenged, along with a similar group of non-vaccinated cows, by conjunctival instillation of a virulent strain of B. abortus biotype 1. Cows in Group 1 received 1/20th and those in Group 2 received 1/400th the recommended dose of strain 19. Marked reduction in the serological response to vaccination was seen only in Group 2. Four cows in Group 1 excreted strain 19 after parturition, one of them aborted and another calved prematurely with heavy infection of the placenta and foetus with strain 19 in both cases. Resistance to challenge was similar in both vaccinated groups, and higher than previously demonstrated after conventional calfhood vaccination with strain 19. It is concluded that pregnant cows can be effectively vaccinated by the subcutaneous administration of a dose of strain 19 vaccine containing approximately 3 times 108 organisms without undue interference with subsequent serological tests or inconvenience resulting from persistence of strain 19 infection.