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

Inforce 3 showed modest pulmonary protection advantages over Nasalgen in maternally immune calves challenged with BRSV.

This randomized controlled trial compared the clinical, immunological, and pulmonary responses to virulent BRSV challenge in colostrum-fed, seropositive Holstein calves vaccinated intranasally with one of two commercially available products: Nasalgen (vaccine A, n=17) or Inforce 3 (vaccine B, n=17). Calves aged 9–20 days were vaccinated and challenged with virulent BRSV nine weeks later. Outcomes assessed included daily clinical scoring, arterial partial pressure of oxygen (PaO2) on day 6 post-challenge, percentage pneumonic lung involvement at necropsy (day 8), viral shedding, and mucosal and systemic antibody responses. Both vaccine groups demonstrated minimal clinical disease and low nasal BRSV shedding following challenge. However, vaccine B calves exhibited lower median lung lesion scores (2.3% vs. 4.6%) and numerically higher median PaO2 values (91.0 vs. 82.8 mmHg), though the latter difference did not reach statistical significance. Notably, 71% of vaccine B calves maintained PaO2 within the normal range compared to only 41% of vaccine A calves. Both vaccines elicited anamnestic mucosal and systemic antibody responses, confirming immunological priming. The study concludes that while both intranasal BRSV vaccines provide adequate protection against clinical disease in maternally immune calves, Inforce 3 demonstrated a modest but potentially clinically relevant advantage in limiting pulmonary pathology and preserving arterial oxygenation. These findings are relevant for bovine practitioners selecting respiratory vaccination protocols in young dairy calves with maternal antibody interference.

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