Immunizing animals in the wild against Brucella (B.) abortus is essential to control bovine brucellosis because cattle can get the disease through close contact with infected wildlife. The aim of this experiment was to evaluate the effectiveness of the B. abortus strain RB51 vaccine in protecting infection as well as vertical transmission in Sprague-Dawley (SD) rats against B. abortus biotype 1. Virgin female SD rats (n = 48) two months of age were divided into two groups: one group (n = 24) received RB51 vaccine intraperitoneally with 3 ¡¿ 10¹⁰ colony forming units (CFU) and the other group (n = 24) was used as non-vaccinated control. Non-vaccinated and RB51-vaccinated rats were challenged with 1.5 ¡¿ 10⁹ CFU of virulent B. abortus biotype 1 six weeks after vaccination. Three weeks after challenge, all rats were bred. Verification of RB51-vaccine induced protection in SD rats was determined by bacteriological, serological and molecular screening of maternal and fetal tissues at necropsy. The RB51 vaccine elicited 81.25% protection in SD rats against infection with B. abortus biotype 1. Offspring from rats vaccinated with RB51 had a decreased (p £¼ 0.05) prevalence of vertical transmission of B. abortus biotype 1 compared to the offspring from non-vaccinated rats (20.23% and 87.50%, respectively). This is the first report of RB51 vaccination efficacy against the vertical transmission of B. abortus in the SD rat model.