Towards control and eradication of BVD [bovine virus diarrhoea]

An ongoing project initiated primo 1992 and aiming at the elucidation of the possibilities to control and eradicate BVD, includes all 113 cattle herds on the island of Samsu. All 3,698 animals over 3 months of age were blood-tested and examined for BVD virus and antibody using two newly developed ELISA methods. Four percent of beef herds and 30% of dairy herds had PI animals. Persistently infected (PI) animals were removed and measures were taken to prevent reintroduction of the infection. Subsequent examinations in the autumn and winter 1992/93 revealed that new PI animals had appeared in 3 herds. However, these animals already were present in the herds at the time of the initial examination, being either PI calves under 3 months of age or PI fetuses and therefore not tested. None of the dairy herds, but 30% of the beef herds were totally without antibody positive animals. The results convincingly demonstrated that BVD can be controlled using sare tests and the applied measures. All 369 dairy herds on the islands of Bornholm and Mors were included in another project with the aim to determine the value of a tank milk antibody test with respect to its ability to indicate the infection status of the individual herds. The above antibody EUSA (a blocking ELISA) was used to test both tank milk samples and blood samples from the herds. Nine animals from each herd were tested, i.e. 2 first parity cows, 2 second parity cows, 2 third parity cows, and 3 calves aged 8-10 months. On basis of the results, the herds were divided into four infection status calegories, i.e. where the calves were antibody positive (status IV), where the calves were antibody negative and 5 or 6 of the cows antibody positive (status III), where the calves were antibody negative and 3 or 4 of the cows were positive (status II), and where none or only 1 or 2 cows were antibody positive (status I). A very good correlation was demonstrated between the infection status of the individual herd and the reaction in a tank milk sample recorded as the percentage of blocking obtained. Tank milk samples from all Danish dairy herds are now being tested in the first quarter of 1994. All farmers are adviced to introduce general BVD infection prophylaxis and to perform a blood test of up to 9 animals in order to confirm lhe infection status indicated by lhe tank milk reaction. Generally, all farmers are adviced to clear herds of PI animals