Foetal Protection against Bovine Virus Diarrhoea Virus after Two-step Vaccination

Summary In order to assess the efficacy of a two‐step vaccination protocol with respect to foetal protection against transplacental infections with bovine virus diarrhoea virus (BVDV) with special attention to BVDV‐2 seronegative heifers were vaccinated with an inactivated BVDV‐1 vaccine and boostered with a modified live BVDV‐1 vaccine after 4 weeks. A second group was left unvaccinated as control. Between days 30 and 120 of pregnancy the heifers of both groups were intranasally challenged with a mixture of BVDV‐1 and ‐2. All heifers of the vaccinated group gave birth to nine clinically healthy, seronegative (precolostral) and BVDV‐free calves. In contrast in the control group four BVDV viraemic underdeveloped calves were born. Additionally, one calf was stillborn and another viraemic calf was not viable and died 2 days after birth. All six calves of the control group were viraemic with BVDV‐2. This study demonstrated for the first time that two‐step vaccination of breeding cattle with a modified live BVDV vaccine 4 weeks after application of an inactivated BVDV vaccine was capable of providing a foetal protection against transplacental infection with BVDV‐2.