Abstract
Objectives
To determine efficacy of orally administered Brucella abortus vaccine strain RB51 against virulent B abortus challenge exposure in cattle as a model for vaccination of wild ungulates.
Animals
20 mixed-breed beef cattle obtained from a brucellosis-free herd.
Procedure
Sexually mature, Brucella-negative beef heifers were vaccinated by mixing > 1010 viable RB51 organisms or diluent with their feed. Heifers were fed individually and consumed their entire ration. Each heifer received approximately 3×1010 colony-forming units (CFU). Six weeks after oral vaccination, heifers were pasture-bred to brucellosis-free bulls. At approximately 186 days' gestation, heifers were challenge exposed conjunctively with 107 CFU of virulent B abortus strain 2308.
Results
Vaccination with the rough variant of B abortus RB51 did not stimulate antibodies against the O-polysaccharide (OPS) of B abortus. After challenge exposure and parturition, strain 2308 was recovered from 80% of controls and only 20% of vaccinates. Only 30% of the vaccinates delivered dead, premature, or weak calves, whereas 70% of the controls had dead or weak calves.
Conclusions
Cattle vaccinated orally with the rough variant of B abortus strain RB51 develop significant (P< 0.05) protection against abortion and colonization and do not produce OPS-specific antibodies.
Clinical Relevance
Results encourage further investigation into use of strain RB51 to vaccinate wild ungulates (elk and bison) orally. (Am J Vet Res1998; 59:1575-1578)Vol 59, No. 12, December 1998
