NATURAL INFECTION WITH BOVINE VIRUS DIARRHEA VIRUS IN A DAIRY-HERD - A SPECTRUM OF SYMPTOMS INCLUDING EARLY REPRODUCTIVE FAILURE AND RETAINED PLACENTA

The consequences of natural infections by bovine virus diarrhoea virus (BVDV) in a dairy herd comprising approximately 60 cows were studied over a 3 year period. The outcome of 39 pregnancies after artificial insemination or natural service during a 4 month period of risk for contracting BVDV was nine abortions, one mummified foetus, one still-birth, three calves that died within 1 week of age, 12 calves persistently infected (PI) with BVDV (11 males and one female) and 13 non-PI calves. Retrospective studies showed that only two of the 13 dams (15.4%) of non-PI calves had been inseminated once, which is a significantly (P<0.001) lower rate than for 192 other gestations (66.7%) during the 3 year period. The gestational duration of multiparous cows (but not of heifers) was longer (P<0.01) for five cows with PI calves (mean +/- SD 287.6 +/- 9.5 days) than for 53 other gestations in 35 cows (280.6 +/- 3.8 days). Five of the 12 dams of the PI calves had not expelled the foetal membranes within 2 days after calving, which is a higher (P<0.001) incidence than the seven cases of retained placenta observed after 198 other calvings. Furthermore, there was a 4.4-fold higher risk (P<0.01) of treatment for enteritis and/or pneumonia in calves and a 6.0-fold higher risk of calf mortality associated with the introduction of BVDV. The mean heart girth of the PI calves was less (P<0.05) than that of non-PI calves, at both 80 and 180 days of age.