[Experiences with a BVD-free transhumance in the summer of 2006]

The aim of this paper was to examine the effect of eliminating persistently infected (PI) animals on BVDV infection during transhumance and to identify possible weak points in the prevention of new infection. An initial blood sample (A) was taken from all the animals until one week before the date of trans-humance (n = 190) and examined for virus by means of real-time RT-PCR or antigen-ELISA and for antibodies by means of ELISA. One PI animal was identified and eliminated. On the day of transhumance (B), serology was performed of the blood samples of all animals that had had a negative or unknown antibody status (n = 93) when blood sample A had been examined. At the end of the transhumance season (C) those animals that had tested seronegative in sample B were re-examined for antibodies (n = 65). The case incidence per animal year amounted to 37.1% up to sample A, 41.8% between sample A and sample B (4 seroconversions). Four cases of seroconversion were diagnosed during the transhumance season, which equalled a case incidence of 17.8% per animal year. A season of transhumance free of PI animals failed to completely prevent BVDV infection, but the new infection rate was significantly diminished. The most possible explanation for new infections are abortions of PI-animals.