A total of 2,194 bulk-tank milks from dairy farms were investigated, and of which 842 dairy farms (55,263 cattle) were assessed to detect persistently infected (PI) individual cattle by performing ELISA. Reverse transcription (RT)-PCR and immunohistochemistry (IHC) were used to develop a rapid screening test for detecting Bovine viral diarrhoea virus (BVDV) in ear tissues. Testing for the bulk-milk tank from dairy farms showed that 2,007 (91.5%) out of a total of 2,194 farms were determined to be positive for BVDV, while only 187 bulk-milk tanks (8.5%) were negative. A total of 55,263 cattle were tested for BVDV, of which 669 (1.2%) cattle from 387 farms (46%) were identified as PI. The distribution of PI was 178 (65.4%) of 272 herds under 14 months. A 220 (80.9%) herds were found in less than 23 month ages. Four infected herds were identified as PI based on RT-PCR analysis. BVDV protein was shown to be localized within epidermal hair bulb cells. This approach of targeted testing of dairy herds using ELISA and RT-PCR for pre-diagnostic testing proves to markedly reduce BVDV-infected herds in Korean dairy farms and in Korean Native Cows.
Challenges for bovine viral diarrhoea virus antibody detection in bulk milk by antibody enzyme-linked immunosorbent assays due to changes in milk production levels