Effect of intranasal vaccination against bovine enteric coronavirus on the occurrence of respiratory tract disease in a commercial backgrounding feedlot.

OBJECTIVE: To measure antibody titers against bovine coronavirus (BCV), determine frequency of BCV in nasal swab specimens, and compare calves treated for bovine respiratory tract disease (BRD) between those given an intranasally administered vaccine and control calves.
DESIGN: Randomized clinical trial. ANIMALS: 414 heifer calves. PROCEDURE: Intranasal BCV antigen concentration and antibody titer against BCV were measured on entry to a feedlot. Calves were randomly assigned to receive 3.0 mL of a modified-live virus vaccine against bovine enteric coronavirus and rotavirus or 3.0 mL of saline (0.9% NaCl) solution. Calves were confined to 1 of 2 pens, depending on vaccination status, for a minimum of 17 days of observation (range, 17 to 99). Selection of calves for treatment of BRD and scoring for severity of disease were done by veterinarians unaware of treatment status.
RESULTS: Intranasal BCV (125/407 [31%]) and serum antibody titers > or = 20 against BCV (246/396 [62%]) were identified in calves entering the feedlot. Vaccination was associated with significant decrease in risk of treatment for BRD; intranasal BCV on entry to the feedlot was associated with increased risk of treatment. Univariate analysis revealed that control calves with intranasal BRD on entry to the feedlot and those with antibody titer < 20 were significantly more likely to be treated for BRD. CONCLUSIONS AND CLINICAL RELEVANCE: These data provide further evidence of an association between BCV and respiratory tract disease in feedlot calves. An intranasally administered vaccine appeared to reduce risk of treatment for BRD.