Effectiveness of the RB51 vaccine in controlling brucellosis in adult beef cows

Seropositive cows were still detected in both vaccinated and control groups at 90 days. However, no new infections were detected in G1 at 180 days or in G1 and G2 at 270 and 360 days, whereas new seropositive cows were diagnosed in all exams in G3 (control). Therefore, the cumulative number of new infections was lower in vaccinated than in control cows (0.2% and 0.0%, vs. 3.2% for groups G1, G2, and G3 respectively; <i>p</i> = 0.0002). In farm A the number of days open was greater in the control than in vaccinated groups (<i>p</i> < 0.05), and in farm B the pregnancy rate was lower in the control than in the group vaccinated once (<i>p</i> < 0.05). In summary, vaccination with RB51 in beef cows reduces the occurrence of new cases of brucellosis and improves the reproductive performance. There is no indication that a second immunization, six months after the first, enhances protection or reproductive efficiency.