[Analysis of bulk milk samples using polymerase chain reaction: an additional tool for bovine viral diarrhea...

Programmes for the eradication and control of infections with bovine viral diarrhea virus (BVDV) concentrate on the identification and elimination of persistently infected (PI) animals. The identification of these animals is mainly based on the detection of viral antigen using ELISA techniques. Protocols detecting viral nucleic acid using RT-PCR have been described recently. Due to high costs the German model recommends screening of animals of 9 up to 36 months of age. Screening of bulk milk samples using RT-PCR technology would allow a system independent of age. The aim of the present study was to test whether bulk milk samples (1433 including max. 50 animals each) collected in four counties of Lower Saxony are suitable for a complementary identification of PI animals via RT-PCR. Thirty-one bulk milk samples derived from 27 dairy herds were BVDV positive, corresponding to 2.3 % of the herds analysed in this study. Two samples first scored doubtful. Follow up tests revealed lactating PI animals in most cases (18). In other cases the epidemiological status of the herd, i.e. high sero-prevalence and/or presence of PI animals among non-lactating cattle, suggested a transient infection detected in the first bulk milk sample. These results demonstrate that monitoring of lactating cattle of any age using RT-PCR is a very sensitive, economically effective additional method for the identification of PI animals.