Brucella suis infection in pregnant cattle

Six pregnant, Bos taurus cows with stages of gestation ranging from 11 to 33 weeks were each inoculated into the right conjunctival sac with 0.2 ml of a smooth culture of Brucella suis type I containing 27 x 10(6) viable organisms. The 6 cows produced 7 calves of which one single calf and one twin calf were stillborn, the cause of which was not determined. Br. suis was not isolated from any of the cows or calves using either special media or guinea pig inoculation. No abnormality was found in any of the cows or calves at autopsy. Microscopic examination of placentas and tissues from stillborn calves revealed no abnormality. Serologically, 2 weeks after inoculation all 6 cows had positive reactions to the Rose Bengal Test (RBT) and serum agglutination (SAT) titres of 25 iu to 116 iu. However, these reactions disappeared within 11 weeks. Only 2 cows had a complement fixation (CFT) titre which lasted a maximum of 5 weeks and reached a titre of 4/4. Following the anamnestic use of Br. abortus strain 45/20 vaccine on 3 of the cows, positive RBT reactions, SAT titres of 33 iu, 29 iu and 58 iu and CFT titres of 4/16, 1/8 and 3/8 respectively were recorded 6 weeks after vaccination.