Porcine respiratory disease complex (PRDC) is prevalent year-round on large-scale pig farms. Pigs cough, wheeze, develop fevers, and die or are culled, resulting in heavy losses, frequent mixed infections, and difficult treatment.
01 How are the three barriers breached?
Healthy pigs have three layers of respiratory defense, providing protection at each level:
Nasal mucosa: Warms and humidifies inhaled air and traps dust and pathogens. The main causes of damage to this barrier are atrophic rhinitis, pseudorabies, and classical swine fever.
Tracheal and bronchial barrier: The directional beating of the mucociliary lining, together with coughing, expels foreign matter, while mucus with antibacterial properties is also secreted. Mycoplasma pneumonia mainly damages this barrier.
Alveolar defense barrier: Macrophages in the lungs and interferons are responsible for engulfing and clearing pathogens. PRRS mainly damages this barrier.
If any one of the three barriers is damaged, pathogens have an opening to break through. Once PRRS breaches the alveolar barrier—the “last line of defense”—the door to secondary infections is open. This is also why mixed infections on pig farms become increasingly complicated to treat.
02 Common pathogens: how to identify them
In the same pig barn, the causes behind “coughing and labored breathing” may be completely different. Compare them one by one to narrow down the possibilities.
Classical swine fever: damages capillaries and increases permeability, causing septicemia, hemorrhage, or necrosis in tissues and internal organs throughout the body; increased eye discharge; constipation or diarrhea.
PRRS: damages pulmonary macrophages and weakens immunity, effectively opening the door to secondary infections; reproductive disorders and endometritis in sows, more respiratory disease in piglets, and interstitial pneumonia seen on necropsy.
Pseudorabies: Mainly inflammation and congestion in the brain; reproductive disorders in sows; egg-drop-like diarrhea, sneezing, and coughing in piglets; and white pinpoint necrotic lesions in the liver and kidneys.
Porcine circovirus: Multisystemic wasting in piglets after weaning, anemia, persistent weight loss, low immunity, abnormally enlarged inguinal lymph nodes, pinpoint hemorrhages in the kidneys, atrophied and hemorrhagic lungs with a “rubber lung” appearance, and raised, mound-shaped skin lesions.
Swine influenza: Rapid onset and a high infection rate, with coughing, a runny nose, and fever; however, recovery is rapid and the mortality rate is low, with infection mainly affecting the upper respiratory tract.
Toxoplasmosis: After parasitic infection, toxins are secreted and cause disease, with a high, sustained fever, enlarged internal organs, liver hemorrhage and necrosis, and interstitial pneumonia accompanied by a gelatinous, transparent substance.
Eperythrozoon: destroys red blood cells, causing jaundice, pallor due to anemia, bleeding from the pores, thin blood, and enlarged, soft liver, kidneys, and spleen.
Mycoplasmal pneumonia: persistent dry cough, normal body temperature, and symmetrical “shrimp-like” lesions in the cardiac and apical lung lobes at necropsy.
Glässer’s disease: a typical secondary disease, often secondary to PRRS, Mycoplasma, etc.; joint swelling, polyserositis, and adhesions in the thoracic and abdominal cavities.
Porcine contagious pleuropneumonia: difficulty breathing, dog-sitting posture while breathing, bleeding from the mouth and nose, and thoracic adhesions.
Pasteurellosis (swine pneumonia): throat swelling, difficulty breathing, and lobular pneumonia.
Reminder: Many cases in the field involve a mix of several pathogens. Symptoms alone can only narrow down the possibilities; confirmation requires laboratory testing (PCR, antibody testing, and bacterial isolation). If you are unsure, do not guess.
03 Medication approach: two commonly used clinical combination regimens
The following are common clinical combination-regimen approaches, provided for reference. Specific medication use should follow the guidance of a licensed veterinarian and be based on the product instructions and antimicrobial susceptibility results. Observe the withdrawal period. This educational content does not constitute a prescription.
Formula one: Compound amoxicillin + electrolytes and multivitamins + Bupleurum + calcium carbasalate — focused on influenza. Compound amoxicillin controls secondary bacterial infections; electrolytes and multivitamins provide nutritional support to aid recovery; Bupleurum and calcium carbasalate reduce fever and relieve symptoms.
Formula two: Florfenicol + doxycycline + calcium carbasalate — focused on infectious pleuropneumonia, swine pasteurellosis, and eperythrozoonosis, among others. Florfenicol and doxycycline are commonly combined for mixed respiratory infections and have broad coverage; calcium carbasalate reduces fever and inflammation.
Key points for use:
Follow the product instructions and veterinary guidance for dosage and course of treatment. Do not increase the dose or combine products without authorization.
Observe the withdrawal period and stop medication as required before livestock are sent to slaughter.
The environment must also be improved while medication is being used (ventilation, ammonia reduction, and temperature control); otherwise, the medication’s effectiveness will be greatly reduced.
If there is no improvement after continuous medication for 2-3 days, consult a veterinarian promptly for reassessment and, if necessary, conduct an antimicrobial susceptibility test.
04 Prevention and control recommendations: treatment is a remedy; prevention is fundamental.
Immunization: Immunize against classical swine fever, PRRS, pseudorabies, circovirus, and other diseases according to the farm’s standard protocols. Consider adjustments only once immunosuppressive diseases (such as PRRS) are stable.
Environment: Ensure ventilation and air exchange, control ammonia and dust, balance temperature control with ventilation, and reduce stress.
Biosecurity: Quarantine introduced animals, use an all-in/all-out system, and disinfect to prevent pathogens from entering the herd.
Health care: During stress periods such as weaning and herd transfers, provide medication-based health care under veterinary guidance to control common pathogens such as Mycoplasma.
Respiratory syndromes are difficult to treat because the root causes are mixed infections and damaged barriers. First, protect all three barriers, then identify the pathogen characteristics accurately so treatment has a clear direction. Prevention relies on immunity and the environment, while treatment relies on symptom management and timing—address both, and respiratory problems on the pig farm can be kept under control.