Porcine respiratory disease complex (PRDC) is one of the most significant health and welfare challenges in intensive pig production. A combination of viral and bacterial pathogens acting synergistically causes pneumonia, pleuritis, and chronic respiratory compromise. Understanding the agents and risk factors guides effective prevention and welfare-centred management.
Causative Agents
PRDC involves multiple pathogens:
- Porcine reproductive and respiratory syndrome virus (PRRSV): Immunosuppressive; opens the door to bacterial secondary infections; economically devastating
- Swine influenza virus (SIV): Causes acute respiratory outbreaks; usually self-limiting but compromises defence mechanisms
- Mycoplasma hyopneumoniae: Primary cause of enzootic pneumonia (EP); causes chronic coughing, reduced growth, and predisposes to secondary bacterial infection
- Actinobacillus pleuropneumoniae (App): Causes acute, haemorrhagic pleuropneumonia with high mortality; pleuritic adhesions from chronic App infection are a major abattoir finding
- Pasteurella multocida, Bordetella bronchiseptica: Secondary bacterial pathogens exacerbating primary viral/mycoplasmal disease
Welfare Impact
Chronic respiratory disease causes persistent suffering — pigs with pneumonia show reduced activity, poor growth, coughing, dyspnoea, and inappetence. Pleuritic pigs show pain on handling. The slaughterhouse lung scoring system (tracking consolidation, pleuritis) provides welfare outcome data at population level — abattoir feedback enables farm-level improvement.
Prevention Strategies
Vaccination: PRRSV, SIV, Mycoplasma, App, and Pasteurella vaccines are available. Vaccination programmes should be designed with the farm vet based on pathogen prevalence and age-group susceptibility. Sow vaccination provides maternal immunity to piglets; direct piglet vaccination targets key risk periods.
All-in/all-out (AIAO) management: Moving pigs as same-age groups through production stages — with complete cleaning and disinfection between batches — breaks pathogen transmission cycles more effectively than continuous flow production.
Biosecurity: Closed herds, testing of purchased breeding stock, quarantine facilities, and vehicle disinfection reduce pathogen introduction risk.
Housing and ventilation: Reducing pen humidity, ammonia, and airborne pathogen concentration through good ventilation (without draughts) reduces respiratory challenge.
Treatment and Welfare Priorities
Clinically affected pigs must be identified early and removed to sick pens with additional feed and water access and antibiotic treatment where indicated. Pigs remaining in the main group when sick are unable to compete for resources and suffer compound welfare compromise. Pain management (NSAIDs) is indicated for acutely ill pigs showing obvious discomfort.