Cattle Health Section, National Veterinary Institute, PO Box 8156 Dep, Oslo 0033, Norway
A retrospective longitudinal study was conducted to examine whether the exposure of dairy herds to bovine virus diarrhoea virus (BVDV) affected udder health. All Norwegian dairy herds that had experienced a marked increase in the BVDV antibody titres in bulk milk (from a level corresponding to an optical density (OD) <0.25 to >0.55, as determined by an indirect enzyme-linked immunosorbent assay) between two nation-wide herd screening examinations carried out late in 1992 and 1993, respectively, were considered to have been exposed to BVDV during the period between the examinations. The reference group included all dairy herds in which the bulk milk was BVDV antibody-negative or had only very low titres of BVDV antibodies (OD < 0.25) each year from 1992 to 1995. The annual incidence rate of clinical mastitis, the bulk-milk somatic-cell count, and the annual rate of culling because of mastitis in the herds, were compared in the year of BVDV exposure (1993) as well as in a period prior to exposure (from 1988 to 1992) and two years following the year of exposure. In herds exposed to BVDV, there was a 7% increase in the incidence rate of clinical mastitis in the year of exposure, as compared with the nonexposed herds. No significant changes attributable to BVDV exposure were observed in the bulk-milk somatic-cell count or in the rate of culling because of mastitis.
This article was published in Preventive Veterinary Medicine, 43, S. Waage, Influence of new infection with bovine virus diarrhoea virus on udder health in Norwegian dairy cows, 123-135, Copyright Elsevier 2000.