Comparative clinical, immunological, and pulmonary responses to virulent bovine respiratory syncytial virus infection in colostrum-fed, intranasally vaccinated calves.

OBJECTIVE

To compare clinical, pulmonary, and immunologic responses to bovine respiratory syncytial virus (BRSV) challenge in colostrum-fed, BRSV-seropositive calves following administration of 2 commercially available intranasal vaccines.

METHODS

34 male Holstein calves (9 to 20 days old) were randomly assigned to receive vaccine A (Nasalgen; n = 17) or vaccine B (Inforce 3; 17). Nine weeks after vaccination, calves were challenged with virulent BRSV. Clinical observations were recorded daily. Arterial partial pressure of oxygen was measured on day 6 after challenge, and percentage pneumonic lung involvement was assessed at necropsy on day 8. Antibody responses and viral shedding were assessed.

RESULTS

Clinical signs were infrequent and mild in both groups, and nasal shedding of BRSV was low. Median lung lesion scores were lower in calves receiving vaccine B than in calves receiving vaccine A (2.3% vs 4.6%). Arterial oxygen concentrations were numerically higher in vaccine B calves (median, 91.0 mm Hg) than in vaccine A calves (median, 82.8 mm Hg), although this difference was not significant. A greater proportion of vaccine B calves had Pao2 values within the normal range (> 87.1 mm Hg) compared to vaccine A calves (12 of 17 [71%] vs 7 of 17 [41%]). Both vaccines induced anamnestic mucosal and systemic antibody responses.

CONCLUSIONS

Both vaccines were associated with minimal clinical disease following BRSV challenge.

CLINICAL RELEVANCE: Results suggest a modest advantage of vaccine B with respect to pulmonary involvement and maintenance of arterial oxygenation under these experimental conditions.