Bovine Respiratory Syncytial Virus in Calves: Welfare and Prevention

Bovine respiratory syncytial virus (BRSV) is a major cause of severe respiratory disease in young calves, causing significant welfare harm and economic loss on cattle farms worldwide.

Key Facts

BRSV is one of the most common viral pathogens involved in bovine respiratory disease (BRD) complex in calves under six months of age
The virus causes severe inflammation of the lower respiratory tract, leading to hypoxia, breathing difficulty, and in severe cases, death
Clinical signs include rapid, laboured breathing, nasal discharge, coughing, fever, and open-mouth breathing
BRSV infection predisposes calves to secondary bacterial pneumonia, compounding welfare harm
Effective vaccines are available and are recommended for both pregnant dams (to boost colostral immunity) and calves
Outbreaks tend to occur in autumn and winter when calves are housed and viral transmission is facilitated by close contact
Mortality rates in severe outbreaks can reach 10-20% in unvaccinated, susceptible calf populations

Welfare Considerations

BRSV causes some of the most acute respiratory distress observed in farmed animal medicine. Affected calves breathe with visible effort, often extending their necks and breathing through open mouths to maximise airflow through severely inflamed airways. The experience of respiratory distress is recognised as profoundly aversive across species — in calves it causes intense physiological stress alongside the physical discomfort of hypoxia and inflammation. Secondary bacterial pneumonia compounds the suffering and extends the duration of illness. Because clinical signs can progress rapidly from mild to severe, daily monitoring of calf respiratory rate and effort is essential for early intervention. Vaccination programmes, colostrum management, adequate ventilation, and appropriate stocking density in calf housing substantially reduce BRSV incidence and severity, representing the most important welfare preventive measures.

What You Can Do

Farmers: implement BRSV vaccination programmes for pregnant cows and calves as recommended by your veterinarian
Ensure calves receive adequate high-quality colostrum within 2 hours of birth to maximise passive immunity
Monitor calf respiratory rates daily and seek veterinary advice at the first signs of respiratory distress
Optimise calf housing ventilation to reduce airborne viral loads without creating draughts
Support welfare-audited beef and dairy supply chains that require respiratory disease monitoring and treatment protocols