EFFECTS OF INFECTION WITH BOVINE VIRUS DIARRHEA VIRUS ON HEALTH AND REPRODUCTIVE-PERFORMANCE IN 213 DAIRY HERDS IN ONE COUNTY IN SWEDEN

Bulk tank milk samples, collected twice with a 1 year interval, from 2 13 Swedish dairy herds with no vaccination programme against bovine vi rus diarrhoea virus (BVDV), were tested for antibodies to BVDV using a n indirect enzyme-linked immunosorbent assay. The herds were classifie d into four different BVDV groupings based on changes in the estimated prevalence of BVDV antibody-positive cows in the herds. The estimated mean prevalences of BVDV antibody-positive cows were maintained as >8 0% in 58 (27.2%) and as <10% in 84 (39.4%) of the herds. A recent intr oduction of the infection was deemed to have occurred in seven (3.3%) of the herds studied. The BVDV groups were compared with regard to par ameters related to disease and fertility at herd level. Relationships were assessed using logistic and ordinary linear regression analyses. The risks for clinical mastitis, retained placenta and oestrus-stimula ting treatments were higher and the calving intervals were longer in B VDV infected herds, i.e. those herds with an increasing or maintained high prevalence of BVDV antibody-positive cows.