Respiratory disease is one of the most significant welfare and economic problems in pig production globally. Porcine respiratory disease complex (PRDC) — a polymicrobial syndrome involving multiple pathogens acting in concert — causes substantial suffering and mortality in commercial herds.
Pathogens and Welfare Impact
PRDC involves a combination of viral and bacterial pathogens. Porcine reproductive and respiratory syndrome virus (PRRSv) and swine influenza virus (SIV) are primary viral pathogens that suppress immune function and damage respiratory epithelium. Secondary bacterial pathogens including Mycoplasma hyopneumoniae, Actinobacillus pleuropneumoniae, Pasteurella multocida, and Haemophilus parasuis cause pneumonia, pleuritis, and systemic infection in immunocompromised pigs.
Pigs with respiratory disease suffer from dyspnea, fever, anorexia, and lethargy. Severe pneumonia causes distress from impaired breathing. Pleuritis — inflammation of the lung lining — causes acute pain on breathing and is associated with particularly poor welfare outcomes in affected pigs. Chronic, low-grade pneumonia impairs growth and causes ongoing welfare compromise without obvious clinical signs — subclinical disease that is often detected only at slaughter through lung lesion scoring.
Environmental Risk Factors
Housing environment strongly influences respiratory disease risk. Inadequate ventilation — resulting in high ammonia, high CO2, and elevated pathogen load — is the single most important modifiable risk factor. Ammonia irritates respiratory epithelium, impairing local immune defenses. Temperature fluctuations stress the immune system. High stocking density increases pathogen exposure and stress. Addressing these environmental risk factors is a welfare-positive management priority independent of vaccination and treatment approaches.
Vaccination and Disease Prevention
Effective vaccination programs against PRRSv, SIV, and M. hyopneumoniae reduce PRDC disease burden significantly. PRRSv vaccination requires matching vaccine to circulating strains and careful timing relative to PRRS status of the herd. All-in all-out production systems, where pigs of different ages are never mixed, reduce pathogen transmission and welfare costs from respiratory disease compared to continuous flow systems.