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.