Surveillance of cattle herds for bovine virus diarrhoea virus (BVDV)-infection using data on reproduction and calf mortality.

The effect of bovine virus diarrhoea virus (BVDV)-infection on pregnancy rate, on stillbirths and mortality of neonatal calves and the size of newborn calves was evaluated in 8 herds in which persistently infected (PI)-animals had been identified. Data from 9 herds without PI-animals were used as controls. At the time of conception of the oldest PI-animal a significant drop in pregnancy rate to about half the herd average was found. About 6 months later a 3-fold rise in calf mortality was seen. This pattern was found in 4 of the herds. In the remaining 4 herds the pattern was less clear, probably reflecting different immune states of the herds. Rough estimation of the size of newborn calves showed that PI-animals were significantly smaller than normal animals. Monitoring of herds for the above-mentioned parameters may be a means of pointing out herds with PI-animals. Most of the data necessary for such surveillance schemes are already available and may readily be used.