Evaluation of the effect of serum antibody abundance against bovine coronavirus on bovine coronavirus shedding and risk of respiratory tract disease in beef calves from birth through the first five weeks in a feedlot.

OBJECTIVE To evaluate the effect of serum antibody abundance against bovine coronavirus (BCV) on BCV shedding and risk of bovine respiratory disease (BRD) in beef calves from birth through the first 5 weeks in a feedlot. ANIMALS 890 natural-service crossbred beef calves from 4 research herds. PROCEDURES Serial blood samples for measurement of serum anti-BCV antibody abundance by an ELISA and nasal swab specimens for detection of BCV and other viral and bacterial BRD pathogens by real-time PCR methods were collected from all calves or subsets of calves at predetermined times from birth through the first 5 weeks after feedlot entry. Test results were compared among herds, over time, and between calves that did and did not develop BRD. The associations of various herd and calf factors with test results were also evaluated. RESULTS At the calf level, serum anti-BCV antibody abundance was not associated with BCV shedding, but BCV shedding was positively associated with BRD incidence before and after weaning. The mean serum anti-BCV antibody abundance at weaning for a group of calves was inversely related with the subsequent incidence of BRD in that group; however, the serum anti-BCV antibody abundance at weaning for individual calves was not predictive of which calves would develop BRD after feedlot entry. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that serum anti-BCV antibody abundance as determined with ELISA were not associated with BCV shedding or risk of BRD in individual beef calves from birth through the first 5 weeks after feedlot entry.