Associations between herd virus status and morbidity and growth in Swedish dairy calves

Respiratory disease is an important health problem in calves. Bovine respiratory syncytial virus (BRSVO), bovine parainfluenza type 3 (PIV-3), bovine corona virus (BCoV) and bovine viral diarrhoea virus (BVDV) are examples of agents that may be involved. The purpose of this study was to determine the association between the herd status for these agents and the incidence of respiratory disease in calves from birth until 90 days (RESP90), and from 91 days until 210 days of age (RESP210). The association with growth rate from birth to weaning was also to be determined. Data on health and growth in all heifer calves born during one year were recorded in 118 dairy herds in south-west Sweden. Serology on samples from three ~7 month old calves per herd was used to determine the herd infection status. Associations between herd infection status and the herd incidence rate of respiratory disease were analysed by Poisson regression models, while associations with growth rate were analysed by a linear regression model. Herds positive for PIV-3, BCoV and BVDV had significantly higher incidences of RESP90 than negative herds (incidence rate ratios ranging between 1.5 and 1.8), while no difference was found with respect to BRSV status. The incidence of RESP210 was higher for herds positive for BCoV than for negative herds (incidence rate ratio=2.1). Herds positive for BCoV had also a lower weight gain (~8%) than negative herds. These results suggests that infections with PIV-3, BCoV and BVDV are directly or indirectly associated with respiratory diseases in calves in Swedish dairy herds