Clinical picture of active bovine viral diarrhoea infection in commercial bovine productive systems

Abstract

Bovine viral diarrhoea (BVD), one of the most important infectious diseases affecting bovine production systems, is thought to show a subclinical course in most cases, especially in regions that have suffered high BVD prevalence for a long time. However, few studies have assessed this rigorously under non-epidemic conditions. Here we assessed how often active BVD infection in a herd, defined as at least one antigen-positive animal, is associated with clinical signs. Surveying and sampling methods were used to detect BVD infection based on clinical picture. Analysis of 1203 samples of individual animals from 167 herds clinically suspected of BVD infection showed that 33.7% of dairy farms, 30.6% of beef cow-calf farms and 40% of feedlots contained at least one animal positive for BVD viral antigen. Prevalence of BVD infection was 7.7% at the animal level, much higher than the prevalence of 1–3% reported in the literature. This suggests that clinical picture can be useful for detecting active BVD infection, and that infections show a variable clinical course. On dairy farms, the presence of at least one antigen-positive animal was associated with a tendency towards lower fertility and higher rates of stillbirths and calf health problems (P < 0.1). On feedlots, such presence was associated with a tendency to a higher of calf health problems. In beef cow-calf systems, however, the presence of an antigen-positive animal was not associated with any particular sign. These results suggest a higher association of active BVD infections spreading in a herd and clinical pictures at the herd level, particularly in dairy herds.