Respiratory Disease in Pigs: Welfare and Prevention
Disease Complex Overview
Porcine respiratory disease complex (PRDC) is not a single disease but a syndrome involving multiple pathogens acting in concert. Primary pathogens: PRRS virus; PCV2 (porcine circovirus type 2); Mycoplasma hyopneumoniae (enzootic pneumonia). Secondary pathogens: Actinobacillus pleuropneumoniae (APP); Pasteurella multocida; Bordetella bronchiseptica; Haemophilus parasuis; Streptococcus suis. Environmental and management stressors amplify susceptibility: mixing, weaning, overcrowding, poor ventilation, temperature variation.
Welfare Consequences
PRDC causes significant welfare harm: laboured breathing, coughing, fever, anorexia, and reduced growth. Pleuritis and pericarditis (common in APP and PCV2-associated disease) cause severe chest pain. Welfare is compounded by the chronic, insidious nature of enzootic pneumonia: subclinical lung damage reduces feed conversion and growth without obvious clinical signs, but post-mortem examination reveals extensive pneumonic consolidation. Many pigs experience chronic low-grade respiratory welfare compromise that remains undetected on farm.
Ventilation and Environment
Poor ventilation is the most important environmental risk factor for PRDC. Key ventilation parameters: ammonia <20ppm; CO2 <3000ppm; relative humidity 60-70%; temperature appropriate to age and stocking density; and draughts prevented, particularly on young pigs. Air quality monitoring (ammonia meters, CO2 meters) provides objective welfare assessment. Slotted flooring with underpig air supply from slurry channels can deliver cold air directly to lying pigs — a significant welfare concern in winter.
Vaccination and Herd Immunity
Vaccines against key PRDC pathogens: Mycoplasma hyopneumoniae (reduces enzootic pneumonia severity and loss of daily weight gain); PRRS (reduces clinical severity and shedding in endemic herds); PCV2 (highly effective, dramatically reduces PCV2-associated systemic disease and PRDC); APP (reduces acute pleuropneumonia mortality in endemic herds); and combination products. Vaccination programmes must be designed with the farm vet, accounting for age, exposure time, and specific pathogen profile.
Antimicrobial Stewardship in PRDC
PRDC is the largest consumer of antibiotics in pig production. Reducing unnecessary antimicrobial use requires: accurate pathogen identification (PCR, culture) to target treatment; avoiding preventive metaphylaxis without evidence of disease; prioritising vaccination and management over antibiotic treatment; and using narrow-spectrum antibiotics as first choice where effective. Respiratory welfare audits (clinical scoring, post-mortem monitoring at slaughter) quantify the welfare impact and guide targeted improvement strategies.