Serological Monitoring of Brucellosis in Female Calves Born from Infected Herds from Birth to their First Calving

The aim of this study was to determine the frequency of brucellosis contagion of female calves born from seropositive and seronegative cows in brucellosis-infected herds. Brucellosis was monitored by serological analysis of 192 female calves from ten stables. Eight of these stables corresponded to family dairy herds, which had been vaccinated with S19; one was a semi-intensive herd vaccinated with RB51 and the last one was an intensive herd vaccinated with both vaccines. Monthly blood samples were taken from the female calves, from birth up to nine months of age; later, blood samples were taken at 12, 15, 18, 21, 24 months, and during delivery or abortion. Blood samples were analysed with Rose Bengal, rivanol and radial immunodiffusion tests to detect the appearance of seropositivity. A total of 192 female calves were evaluated and only 23% (45/192) were seropositive to brucellosis during the entire study. Of the 45 serologically positive female calves, 47% (21/45) were daughters of seropositive cows, while 53% (24/45) were daughters of seronegative cows. In conclusion, only 23% of the female calves born from infected herds showed seropositivity to brucellosis from birth up to 24 months of age, of which less than half were daughters of seropositive mothers and more than half were daughters of seronegative mothers. Therefore, serological diagnosis of brucellosis should be considered at an early age, which is currently not regular practice. In addition, biosecurity measures should be established, mainly in family dairy herds.