The aim was to test the efficacy of a modified-live virus (MLV) vaccine in protecting fetuses from infection with type 1 or type 2 Bovine viral diarrhoea virus (BVDV) when pregnant heifers were challenged at approximately 170 d of gestation with noncytopathic field isolates.

Experimental set up
The 83 pregnant heifers had been bred naturally 4 weeks after vaccination. Fetuses were collected 60 days after BVDV type 2 challenge and newborn calves were collected before colostrum intake after BVDV type 1 challenge. Protection was determined by measuring the serum neutralizing (SN) antibody response in the fetus or calf and by virus isolation from thymus, lung, spleen, and kidney tissue samples.

Results
There was a measurable SN antibody response to BVDV in all the fetuses and calves of the control heifers, which had received a placebo vaccine. However, only 4 of 22 calves and 7 of the 28 fetuses of the MLV-vaccinated heifers demonstrated SN antibody after BVDV challenge. Type 1 BVDV was isolated from tissue samples of 5 of the 12 calves of control heifers and none of 22 calves of the MLV-vaccinated heifers challenged with type 1 BVDV. Type 2 BVDV was isolated from tissue samples of 17 of the 18 fetuses of the control heifers and 2 of the 28 fetuses of the MLV-vaccinated heifers challenged with type 2 BVDV.

Conclusion
The results of this study demonstrate that the MLV vaccine reduces the fetal infection rate by at least 82% for BVDV type 1 and by 75% for BVDV type 2 when heifers are exposed to highly fetotrophic BVDV at 170 d of gestation.

[Source: Canadian Journal Veterinary Research (October, 2009)]