Bovine viral diarrhoea (BVD) leads to substantial economic losses in beef and dairy herds worldwide. Two case-control studies were carried out to analyse the impact of BVD virus (BVDV) on fertility in dairy herds in the province of Styria during the Austrian BVD eradication programme from 1996 to 2012. In addition the influence of generic factors (e.g. production area, animal breed, lactation period) was analysed. In study 1, herds in which at least one persistently BVDV-infected (PI) animal was detected (case herds) were compared to a group of control herds proven free from BVDV infection (control herds).
In study 2, the period during which PI animals were present in the case herd (exposed period) and the period in these herds after BVD eradication (unexposed period) were compared. Calving interval (CAI) and the probability of a first service conception (FSC) were used as indicators in a mixed regression model to investigate the impact of BVD on reproductive performance. The model results indicated that BVD had a significant influence on CAI and FSC. The average CAI was 2 days shorter in control herds than in case herds in the first study and the CAI was 7 days shorter in unexposed periods than in exposed periods in the second study. Cows from control herds were 1.1 times more likely to conceive at first service compared to cows from case herds and cows served during the BVDV unexposed period were 1.3 times more likely to conceive at first service than those inseminated during the exposed period. Besides BVD the animal breed and the lactation period showed a substantially impact on the analysed fertility indicators.
BVD / fertility / case-control study / eradication program