A study of Bovine coronavirus (BCV) and Bovine respiratory syncytial virus (BRSV)infections in dairy herds in Sweden

Bovine coronavirus (BCV) and bovine respiratory syncytial virus (BRSV) infections are spread in cattle herds worldwide. When introduced in to a susceptible herd, both infections cause respiratory disease. BCV is also associated with diarrhea in both calves and adult cattle. The purpose of this study was to investigate the seroprevalence of BCV and BRSV in dairy cattle herds in an area of Sweden. Specific goals were to determine the immunity against these infections in both conventional and organic dairy herds during two sampling occasions, and if the prevalence of these infections in conventional herds differ from organic herds. The influence of different risk factors for seropositivity was also investigated. Around 700 serum samples, taken from 20 conventional and 20 organic dairy herds in south eastern Sweden on two sampling occasions with one year interval, were tested by ELISA for presence of antibodies to BCV and BRSV. On individual level, the seroprevalence at both occasions varied between 82-86% to BCV and 79-82% BRSV. Analyzing the data on herdlevel revealed that the conventional herds had a significantly higher mean seroprevalence to BCV and BRSV than the organic (P< 0.001). A significant association was found between age and seroprevalence (P< 0.001). Cows younger than 5 years old in conventional herds had significantly higher mean seroprevalence than the organic (P< 0.001). Only 30% of the youngest cows in organic herds compared to 70% in conventional herds were positive to both BCV and BRSV which increased up to 100% in the oldest cows. The mean absorbance value in positive cows older than 5 years was significantly higher compared with those younger than 5 years (P<0.001). Higher mean titres of antibody in the oldest cows most likely make their enriched colostrum a valuable tool in herds with neonatal infection problems. This study suggests that organic management may be associated with a lower incidence of BCV and BRSV infections compared with conventional management.