There is not a clear correlate with mechanisms of protection. In contrast to the predominant role of cell-mediated immunity in protection against smooth Brucella species, several studies showed that antibodies play a predominant role in protective immunity to B.ovis in mice and rams. Immunization with detergent-extracted recombinant Omp31 induced bactericidal antibodies against outer membrane proteins and rough lipopolysaccharide which are able to kill B.ovis in the presence of complement.