Growth Rates of Vaccinated and Unvaccinated Weaner Angus Cattle in BVDV Endemic Herds in Southern NSW

In Australia Bovine Viral Diarrhoea Virus (BVDV) is considered to be primarily associated with reproductive losses in cattle. Trials in two BVDV endemically infected beef herds in southern NSW were undertaken to assess the impact of exposure to BVDV on weight gain in young recently weaned cattle. The study, comprising 410, 6-15 month old animals (Property 1), and 120, 7-15 month old animals (Property 2), compared growth rates between vaccinated and control animals during ongoing exposure to known persistently-infected individuals. At the commencement of the trial, 70% (Property 1) and 68% (Property 2) of the animals were antibody-positive. At the end of the trial, almost all animals were antibody-positive, either as a result of natural exposure or vaccination, or both. Predicted mean weight gain for Vaccinate animals compared to Control animals was 0.25 kg lower on Property 1 and 4.2 kg greater on Property 2, these differences being non-significant. Comparison of animals which consistently tested antibody positive and those animals that seroconverted from antibody negative to antibody positive did not show any significant difference in weight gains. The results from this trial provide evidence that vaccination against BVDV in young (6 – 15 months) beef cattle in endemic herds grazing at pasture does not result in increased growth rates.