The core challenge facing biosecurity on pig farms in autumn and winter can be summed up in one sentence: pathogens survive longer at low temperatures, while disinfection becomes less effective.
African swine fever virus can survive for 60 to 1000 days in materials such as soil, feed, and transport vehicles, and low temperatures further extend its survival window. Meanwhile, research shows that when the temperature drops from 20℃ to 0℃, the bactericidal effectiveness of most disinfectants decreases by more than 50%. In winter, pig barns are made more airtight to retain heat, causing ammonia and dust concentrations to rise. The pigs’ respiratory mucosal barriers are continually damaged, weakening local immunity. On one side, viruses survive longer; on the other, disinfection efficiency drops sharply, with a group of pigs whose resistance is also reduced in between. If autumn and winter biosecurity still follows the summer plan, it is like running around unprotected under the illusion of disinfection.
The key to biosecurity is not how many measures are taken, but whether each measure remains effective under low-temperature conditions.
I. Disinfection: Completely replace the “summer protocol”
The first principle of winter disinfection is to select disinfectants according to temperature, not by area of the facility.
When the temperature outside the barn is above -6°C, a 0.5% glutaraldehyde aqueous solution may be used; below -6°C, it is necessary to switch to a disinfectant specifically formulated for low temperatures, such as 0.2%–0.3% sodium dichloroisocyanurate or 0.2%–0.5% potassium peroxymonosulfate compound. Potassium peroxymonosulfate still achieves a kill rate of 99.9% against classical swine fever virus at 0°C. Its solubility changes little at low temperatures, and its oxidizing capacity remains stable, making it a reliable choice for disinfection outside barns in winter. For disinfection of the indoor environment, a 0.2%–0.5% potassium peroxymonosulfate compound may be used, but disinfection with pigs present is not recommended in winter and spring.
Disinfectants must be prepared using warm water at 20–30°C. This not only improves solubility but also enhances the disinfectant’s activity. When the air temperature is below 0°C, add 1%–3% sodium chloride or calcium chloride to the disinfectant solution as an antifreeze to prevent it from freezing and becoming ineffective. Schedule disinfection on a sunny day from 10 a.m. to 3 p.m., when temperatures are relatively higher and the disinfectant works most effectively.
Another easily overlooked detail: organic matter must be thoroughly removed before disinfection. Manure and feed residue can form a protective film at low temperatures. Experimental data show that when organic matter is present, the penetration time of disinfectants in winter needs to be extended by 50%–100%. In winter, manure and wastewater adhere more strongly, so cleaning takes 30% longer than in summer. Clean thoroughly before disinfecting; otherwise, the disinfectant is just “bathing” the manure and wastewater.
II. Personnel, Vehicles, and Supplies: Low Temperatures Magnify Every Weak Point
Personnel management is the first line of defense for winter biosecurity. For 3 days before entering the farm, personnel must not visit high-risk locations such as pig farms, slaughterhouses, or agricultural markets. Before entering, they must complete the full process of changing shoes, disinfection, showering, and changing into on-site clothing. Personal belongings may be brought in only after ultraviolet or fogging disinfection. Personnel on site should have fixed roles and minimize movement between barns—the reduced ventilation inside barns in winter makes the risk of cross-contamination by pathogens in enclosed spaces higher than in summer, and low temperatures magnify the cost of moving between work areas.
Vehicle risks are especially pronounced in winter. Pig transport trucks and feed trucks are typical “mobile sources of contamination.” Low temperatures in winter make it difficult for vehicles to dry after washing, and incomplete drying greatly reduces the effectiveness of disinfection. The standard procedure is to establish a washing and disinfection center 1–3 kilometers outside the farm. After pre-cleaning, high-pressure washing, and disinfection, vehicles enter a drying room and are dried at 65–75°C for 45–60 minutes to ensure pathogens are thoroughly eliminated. Where feasible, pig farms should have feed trucks unload at a designated location outside the farm, and prohibit all outside vehicles from entering the farm. Pig transport trucks must be washed, disinfected, and dried immediately after use—don’t “wait until there’s time.”
Disinfection of supplies should distinguish between items that “can be heat-treated” and those that “cannot be heat-treated.” After supplies arrive, first let them return to room temperature before treatment. Give priority to disinfection by heating (60～70℃ for 30 minutes); for supplies that cannot be heat-treated, prepare a disinfectant solution with warm water at 25℃ and soak them for at least 30 minutes. In winter, the outer packaging of supplies may develop condensation during low-temperature transport. Moist surfaces accelerate pathogen attachment, so the drying step before entry must not be skipped.
Three. Introduction and quarantine: proactively adjust the pace of introductions in winter
Introducing breeding stock is necessary to refresh a pig farm’s genetic lines, but it is also the most vulnerable link in the winter biosecurity chain. In low temperatures, transport causes greater stress, the herd takes longer to adapt after arrival, and pathogens introduced with the animals are more likely to “take hold” when the herd’s resistance is at its lowest.
The strategy for northern regions should be “bring in enough replacements early, and do not bring in pigs during winter.” It is recommended to bring in a sufficient number of replacement pigs in one batch before 11 each year, and not to bring in any more pigs from 3 to 4 of the following year, cutting off the high-risk winter introduction route at its source. If introducing pigs is truly necessary, strict testing must be carried out three times ( 1 weeks before introduction, 1 weeks after arrival, and 1 weeks before joining the herd). The quarantine facility should be located upwind and more than 100 meters from the production area, with independent access routes and tools. The quarantine period should be no shorter than 28 to 45 days. Sampling and testing should be repeated before the end of quarantine, and pigs may join the herd only after key pathogens are confirmed negative. Insulation and ventilation in winter quarantine facilities must be adjusted and tested in advance; otherwise, pigs in quarantine are more prone to health fluctuations under cold stress, turning “quarantine” into “latent infection.”
IV. Airborne transmission barriers: a transmission route that cannot be ignored in winter
Airborne transmission of African swine fever has been confirmed in field trials. Fluorescent powder tracing has confirmed that dust and aerosols can spread from one barn to another. In winter, pig barns are more enclosed and ventilation is reduced, extending the time aerosols remain inside the barns and making this route riskier than in summer.
In positive-pressure filtration trials in grower-finisher barns, the air filtration system achieved a blocking and preventive effect of 90%, with a retention rate of 84.96%. However, air filtration is not a “install it and forget it” solution. Filter replacement, differential pressure monitoring, and ongoing system maintenance determine whether it truly blocks pathogens or merely provides psychological reassurance. For farms that cannot install whole-barn air filtration, at a minimum, air inlets should be located away from pollution sources; fan openings and filters should be checked regularly for contamination; and air sampling in abnormal barns should be included in monitoring. When ventilation is reduced in winter, the risk of “internal air recirculation” inside barns increases. Environmental sampling at fan openings can reflect the actual risk level better than floor disinfection.
V. Monitoring and Immunization: The “Last Mile” of Biosecurity
All disinfection and isolation measures ultimately come down to determining whether the herd itself has been infected.
Autumn is a key window for concentrated immunization. Before winter, the immunization coverage and quality of core vaccines for foot-and-mouth disease, classical swine fever, pseudorabies, and diarrhea should be checked. Large-scale pig farms should monitor antibody levels regularly and promptly provide booster immunizations to individuals that do not meet the requirements. But immunization cannot replace monitoring—clinical inspections should be more frequent in winter, with particular attention to slight declines in feed intake, minor fluctuations in body temperature, and increases in the proportions of abortions or stillbirths. Against the background of low-virulence strains circulating, these subtle signs are earlier and more reliable than “a pig suddenly stops eating.” If an abnormal pig is found, isolate it and collect samples for testing immediately, rather than giving it medication first and observing it.
Summary
The core of biosecurity for pig farms in autumn and winter can be summed up in four points: adjust disinfection protocols according to temperature; close every gap in personnel, vehicle, and supply controls that low temperatures can amplify; proactively avoid high-risk windows when introducing breeding stock; and leave no gaps in blocking and monitoring airborne transmission.
Low temperatures do not make biosecurity “impossible,” but they quickly expose every half-hearted measure. Disinfecting once may work in summer. In winter, disinfecting once is equivalent to doing nothing if the wrong disinfectant is selected, the water temperature is insufficient, or organic matter has not been thoroughly removed. In autumn and winter, biosecurity is not about how complex the plan is, but whether every step can still be carried out “effectively” in low temperatures. Turning “done” into “done properly” is the most reliable line of defense this winter. (Source: Zhang Weiguang)