Vaccination with a multivalent modified-live virus vaccine administered one year prior to challenge with bovine viral diarrhea virus type 1b and 2a in pregnant heifers

A total of 85 beef heifers were used to determine if vaccination with a modified-live virus (MLV) vaccine containing bovine viral diarrhea virus types 1 and 2 (BVDV1 and BVDV2) approximately 1 year prior to challenge with virulent BVDV1b and BVDV2a will protect against fetal infection. BVDV1 and BVDV2 seronegative heifers were vaccinated at approximately 15 months of age with a commercially available combination MLV vaccine containing BVDV1a and BVDV2a or placebo; heifers were artificially inseminated approximately 9 months after vaccination. The heifers were challengeinoculated intranasally at 80 to 90 days of gestation with a virulent BVDV1b or BVDV2a virus (i.e., 368 and 374 days post-vaccination, respectively). Clinical signs of BVDV infection including serologic status, complete blood count, rectal temperature, and viremia were monitored for 14 days following challenge. After challenge, vaccinated heifers in the BVDV1b and BVDV2a challenge groups experienced significantly less leukopenia and viremia than control heifers. Fetuses were harvested approximately 70 days following challenge and tissues were collected for virus isolation. All heifers that received vaccine were protected from fetal infection following challenge with BVDV1b or BVDV2a, whereas 15 of 18 (83.3%) and 21 of 22 (95.5%) control heifers had infected BVDV1b and BVDV2a fetuses, respectively. In this study, a combination MLV vaccine containing the minimum immunizing dose of BVDV1a and BVDV2a, with other fractions at release dose or higher, administered 1 year prior to challenge protected against fetal infection in the face of a substantial challenge infection with either BVDV1b or BVDV2a.