After autumn and winter arrive, ambient temperatures gradually begin to fall. Low temperatures prolong the survival of environmental pathogens; temperature fluctuations stress the herd and reduce immunity; the conflict between temperature retention and ventilation amplifies the risk of aerosol/dust transmission; meanwhile, disinfection becomes less effective and vector activity increases.
I. Environmental and in-barn transmission risks
1. The challenge of balancing temperature retention and ventilation increases the risk of aerosol and dust transmission. When pig barns are kept sealed to retain heat, inadequate ventilation allows ammonia, hydrogen sulfide, and dust to accumulate. Pathogens attach to dust and aerosols and spread within and between barns. Diseases such as PRRS, pleuropneumonia, and mycoplasma infections can easily spread through the herd. Forced ventilation, however, can cause drafts and large day-to-night temperature fluctuations, compromising the respiratory mucosal barrier.
2. Low temperatures cause conventional disinfectants to fail. The activity of many disinfectants (aldehydes, phenols, alkalis, and quaternary ammonium compounds) drops sharply below 5℃; disinfection pools and disinfectant solutions freeze, making the disinfection process a mere formality. Damp, cold conditions also keep housing and equipment wet for extended periods, allowing viruses and bacteria to survive (survival times for African swine fever and diarrhea viruses increase significantly at low temperatures).
3. Imbalanced humidity inside the housing. Insufficient ventilation → high humidity, which favors the proliferation of diarrhea-causing pathogens, mold, and bacteria; dry, windy weather → a sharp increase in dust, aggravating respiratory tract damage.
II. Increased risk of transmission by vectors
• Rodents: As outdoor food becomes scarce in winter, large numbers migrate to pig farms, feed stores, and farrowing rooms. They are important mechanical vectors of African swine fever, PRRS, Salmonella, and Toxoplasma; rodent feces and urine contaminate feed and drinking water.
• Wild birds: During the migratory season, wild birds may carry pathogens, and their droppings may land in the farm area, on feed silos, and on roofs, carrying influenza, Salmonella, and other pathogens. Bird feathers and droppings may also contaminate the surrounding environment.
Three. Risk of external introduction via people, vehicles, and materials
1. Increased vehicle risk: At low temperatures, pathogens can survive for a long time on vehicle tires, undercarriages, and in gaps in vehicle compartments. Vehicles dry slowly after washing and disinfection; inadequate washing and disinfection can easily result in pathogens being carried into the farm.
2. Personnel movement risk: As autumn and winter approach, biosecurity pressure in the farm area increases, leading to more frequent staff outings, trips back to their hometowns, and purchasing. Pork and cooked foods from outside the farm, fresh produce, and express delivery parcels may carry pathogens.
3. Supply risk: the outer packaging of feed, veterinary medicines, consumables, and cold-chain supplies may be contaminated with pathogens; the temperature in the supplies’ stationary disinfection warehouse is low, reducing the effectiveness of fumigation disinfection.
Four. Internal risks within the pig herd and high incidence of priority diseases
1. Porcine respiratory disease complex (PRDC): mixed infection with PRRS, Mycoplasma, contagious pleuropneumonia, Glässer’s disease, and Pasteurella; coughing, labored breathing, abdominal breathing, and increased mortality and culling. Temperature-difference stress is the main trigger.
2. Viral diarrhea (PED/TGE): high incidence in farrowing and nursery units. Diarrhea viruses are highly stable at low temperatures; once introduced onto the farm, they can easily circulate in the farrowing unit, causing high piglet mortality. Stress from regrouping and weaning can fuel outbreaks.
3. Foot-and-mouth disease: The virus remains stable in low-temperature environments and spreads through contact and aerosols; cases are more common in autumn and winter.
4. African swine fever: Highly tolerant of low temperatures; multiple routes—including vectors, vehicles, and supplies—can compound the risk. Subclinical infection and slow shedding make early detection difficult.
5. Mycotoxin risk: With newly harvested corn coming onto the market, autumn and winter storage can easily lead to dampness and mold, damaging immunity.