Pneumonia is the leading cause of calf mortality after the neonatal period, causing significant welfare harm and economic losses across dairy and beef enterprises. Understanding the multifactorial causes of bovine respiratory disease (BRD) enables targeted prevention strategies.
Pneumonia causes genuine suffering in calves — fever, respiratory difficulty, lethargy, and pain from pulmonary inflammation. Calves with clinical pneumonia show reduced feed intake, weight loss, depressed behaviour, and nasal discharge. Severe cases cause respiratory failure and death. Even calves that recover from clinical disease may have permanent lung damage, impairing their productive potential and potentially causing ongoing chronic welfare compromise. The suffering of calves with undetected or delayed-treatment pneumonia is a preventable welfare failure.
BRD is a polymicrobial disease typically involving: viral triggers (Bovine Respiratory Syncytial Virus, Bovine Herpesvirus 1, Parainfluenza-3, Bovine Coronavirus) that damage airway defences and enable secondary bacterial infection, followed by bacterial pathogens (Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis). Mycoplasma bovis is particularly problematic due to antibiotic resistance and its ability to cause severe, chronic lung damage and joint disease. Understanding the pathogen profile in a specific enterprise guides vaccination and treatment choice.
Key risk factors for calf pneumonia: poor colostrum management (failure of passive transfer leaves calves immunocompromised), mixing calves of different ages and sources (introducing new pathogens), inadequate ventilation in calf housing (high humidity, poor air exchange, high bacterial and viral loads), high stocking density, nutritional stress (restricted milk feeding), cold stress (particularly in young calves), and weaning stress. The 'triangle' of host susceptibility (poor immunity), pathogen challenge (high pathogen load), and environmental stress (cold, poor ventilation) explains most BRD risk.
Early detection is critical for welfare — calves treated within 24 hours of first signs have significantly better outcomes than those treated after 48+ hours. Clinical Respiratory Scoring systems (e.g., Wisconsin Respiratory Scoring Chart — assessing rectal temperature, nasal discharge, eye discharge, ear position, cough on stimulation) provide standardised criteria for treatment decisions. Training stockpeople in recognising subtle early signs (reduced activity, slightly depressed ears, slightly elevated respiratory rate) before obvious illness occurs is a welfare investment.
Treatment includes: appropriate antimicrobials (selected based on pathogen, antibiotic sensitivity, and residue considerations), NSAIDs for pain relief and anti-inflammatory effect (significantly improving welfare outcomes and recovery rates — NSAID treatment should be part of every pneumonia treatment protocol), and supportive care. Re-treatment protocols for non-responders and anti-inflammatory use in severe cases improve outcomes. Treatment records enable assessment of drug efficacy and inform future antibiotic stewardship decisions.
Prevention strategy: maximise passive immunity (target ≤20% FPT rate), vaccination against viral components (intranasal vaccines can be given before maternal antibody decline — at 2-3 weeks), optimise ventilation (minimum 4 air changes per hour while maintaining thermal comfort), limit mixing of calves from different sources, implement all-in/all-out management in calf accommodation, and provide adequate nutrition to support immune function. Systematic risk assessment with the attending veterinarian enables targeted prevention investment.