Biosafety of Brucella abortus strain RB51 for vaccination of mature bulls and pregnant heifers

Objective-To determine shedding and colonization profiles in mature sexuall y intact bulls and pregnant heifers after vaccination with a standard calfh ood dose of Brucella abortus strain RB51 (SRB51), Animals-6 sexually mature 3-year-old Jersey bulls and 7 mixed-breed heifers in midgestation. Procedure-Bulls and pregnant heifers were vaccinated IM with the standard c alfhood dose of 3 X 10(10) colony-forming units of SRB51. Alter vaccination , selected body fluids were monitored weekly for vaccine organism shedding. Pathogenesis was monitored in bulls by weekly breeding soundness examinati on and, in heifers, by delivery status of the calf. Vaccine organism coloni zation was assessed by obtaining select tissues at necropsy for bacterial c ulture. Serologic analysis was performed by use of numerous tests, includin g complement fixation, an SRB51-based ELISA, and immunoblot analysis. Results-After vaccination, none of the vaccinated bulls or heifers shed SRB 51 in their secretions. Results of breeding soundness examination far bulls were normal as was delivery status of the pregnant heifers (6 live births, 1 dystocia). At necropsy, SRB51 was not recovered from any of the selected tissues obtained from bulls, heifers, or calves; however, serologic analys is did detect SRB51-specific antibodies in all cattle. Conclusions and Clinical Relevance-Vaccination with the standard calfhood d ose of SRB51 administered IM was not associated with shedding or colonizati on in sexually mature bulls or pregnant heifers. Also, under conditions of this study with small numbers of animals, IM vaccination with SRB51 does no t appear to cause any reproductive problems when administered to sexually m ature cattle.