African swine fever is a highly pathogenic and highly contagious animal disease that severely constrains the stable and healthy development of China’s pig industry. Compared with large-scale commercial farms, small and medium-sized pig farms are constrained by factors such as site conditions, funding, and labor. They commonly have shortcomings such as weak biosecurity foundations and scattered, unsystematic control measures, making it more difficult to implement disease prevention and control. Most current related research focuses on large-scale farms, while practical technical solutions suited to the circumstances of small and medium-sized pig farms are relatively scarce.
Drawing on the transmission characteristics and epidemiological patterns of African swine fever, and based on the production and operational realities of small and medium-sized pig farms, this article systematically reviews key control points for ASF prevention and control across four areas: establishing physical barriers, managing feed and water-source risks, monitoring herd health, and managing transport throughout the process. It sets out standardized operating procedures suited to the entire livestock production chain, with the aim of helping small and medium-sized pig farms establish a low-cost, easy-to-implement, and efficient biosecurity protection system, while also providing a practical reference for disease risk management and the sustainable development of the pig industry.
I. Improve biosecurity infrastructure and establish robust physical protection barriers
Physical isolation barriers are the first line of defense against African swine fever virus entering a farm. Small and medium-sized pig farms should establish a routine fence inspection system and conduct comprehensive monthly inspections of perimeter walls and protective fencing, promptly repairing damaged sections, holes, and gaps between the bottom of walls and the ground. Materials used to repair fences should preferably be UV-resistant and corrosion-resistant galvanized steel sheets or high-density polyethylene panels. Fence openings should be no larger than 2cm, the overall height should be at least 1.8m, and the bottom of the wall should extend at least 30cm below ground to prevent wild animals such as rodents and wild boars from entering the farm. People and vehicles should use separate routes within the farm. Clean and contaminated areas must be strictly delineated, with a double-gate access system; the distance between the two gates should be ≥5m. The ground should be finished with nonslip concrete at a 3% slope to ensure one-way drainage of wastewater from contaminated areas and prevent backflow that could cause cross-contamination between clean and contaminated areas.
Strictly implement one-way flow at the pig loading platform and feed unloading area: set the slope of the loading and unloading platform to 15–20°, lay non-slip panels on the platform, and install solid partitions 50cm high to prevent pigs from moving back in the opposite direction. In the feed unloading area, after raw materials are unloaded, they must go directly into sealed conveying pipelines and remain enclosed throughout transport, reducing opportunities for contact with the external environment.
At the same time, establish an integrated prevention and control system for rodents, birds, and pests. For rodent control, use anticoagulant rodenticides (bromadiolone and flocoumafen) in combination with physical trapping. Install 1 fixed bait stations every 10m, equipped with rainproof protective facilities; replenish bait monthly, and monitor signs of rodents every 3 months, keeping the rodent-sign index stable at no more than 5. Fit feed storage building windows with 304 stainless steel bird-proof mesh with a mesh size of ≤1.2cm, and install conical bird-proof covers at least 30cm high on roof vents. Lay a quicklime isolation strip within 5m of the pig house perimeter, using 1.5kg/m²; the strip must be at least 30cm wide. Reapply and rake in the quicklime monthly so it makes full contact with the soil, forming a perimeter protective barrier.
II. Control feed and water sources to cut off transmission through feed and water
Feed is an important transmission vehicle for African swine fever, so controls must cover the entire process, from procurement and storage to use. The use of swill or food scraps from kitchens and dining areas to feed pigs is strictly prohibited. Feed ingredients must be purchased only from suppliers qualified to provide ASF testing that meets requirements. Sample 5% of each batch of ingredients and use fluorescence quantitative PCR to test for viral nucleic acids (detection limit: 10 copies/μL). Ingredients may be stored only after passing the test. Give priority to pellets with a particle size of 3–5mm and hardness of ≥60 N to reduce the risk of viruses being carried by dust. If mash feed is used, it must be screened through a 80-mesh sieve, with the proportion of impurities passing through the sieve kept below 5%, to reduce contamination risks from impurities. Use opened feed bags within 48h wherever possible. Seal any remaining feed in double-layer polyethylene bags, label them with the opening time and remaining quantity, and maintain the storage room at a constant 15–25℃ with relative humidity below 65%. Keep the room dry and well ventilated to prevent feed from becoming moldy or contaminated by pathogens.
Establish a monthly water quality monitoring program for the pig farm water supply system. Each month, collect 500 mL water samples at three points: the water storage tank inlet, the outlet, and the drinking water endpoint in the pig housing. Test for African swine fever virus; the water may be put into use only if the test is negative. Install a 300-mesh stainless steel filter cartridge in the drinking water pipeline (filtration pore size ≥ 0.05 mm). Its filtration efficiency for particles ≥ 50 μm must reach 99%. Equip the filtration system with a backwashing device and flush at a flow rate of 3 m/s for 10 min to prevent filter cartridge clogging from affecting filtration performance. Use sodium hypochlorite with available chlorine ≥ 10% to disinfect the water storage tank, ensuring the disinfectant completely submerges the tank's inner walls. After soaking for 24 h, drain the tank and rinse repeatedly with clean water 3 times. After disinfection, test the free chlorine in the water and maintain it at 2–3 mg/L. Resume water supply once the indicators meet requirements.
Three. Conduct dynamic monitoring of the pig herd and standardize procedures for handling abnormal pigs
Establish a standardized daily inspection and monitoring system for pig herds, with fixed inspection times each day (such as 8 a.m. and 15 p.m.). Focus on observing indicators including feed intake, body temperature, skin condition, and respiratory rate. Measure body temperature using an electronic thermometer. For skin examinations, focus on checking the tips of the ears, groin, and armpits for erythema, congestion, and hemorrhagic lesions. Count chest movements to determine respiratory rate; the normal respiratory rate for pigs is 10–20 breaths/min. Nursery pigs are the priority group for monitoring, with inspections 2 times daily. Conduct special physical examinations of pregnant sows at gestation days 30, 60, and 90.
Sample testing includes three types of samples: dead pigs, environmental swabs, and pigs suspected of being ill. Collect oral and anal swabs from dead pigs. Insert the swab into the sampling site by 3–5cm and rotate it 3 times, then place it in a centrifuge tube containing 5mL of virus preservation solution. For environmental samples, select an area of 10cm×10cm, wipe the floor, walls, and tools in the pig enclosure with sterile cotton swabs, and place them in a centrifuge tube containing 3mL of virus preservation solution. Refrigerate all samples at 4℃ and deliver them to the designated testing institution within 24h for fluorescent quantitative PCR testing (detection upper limit: 10 copies/μL). If a positive result is detected, immediately activate the emergency epidemic isolation plan: designate a core area, buffer zone, and threatened area centered on the positive site. Complete culling and harmless disposal of pigs in the core area within 48h. Impose traffic restrictions in the buffer zone and threatened area, restrict the movement of people and pigs, and conduct continuous monitoring for 21d. Restrictions may be lifted only if no new cases occur.
Dead livestock and poultry can be rendered harmless by using a biochemical pit or biological fermentation. The capacity of the biochemical pit should match the pig farm’s herd size, with a volume of 0.5m³ per pig. Construct it using reinforced concrete at least 20cm thick, cover the opening, and provide a ventilation opening to balance airtightness and ventilation. For biological fermentation, use dedicated microbial agents containing Bacillus subtilis and Bacillus licheniformis. Add 2kg of microbial agent for every 100kg of dead pigs, and maintain high-temperature continuous fermentation at 60–70℃ for 72h to completely inactivate the virus. Dispose of contaminated bedding using combined incineration and deep burial. The incinerator temperature must be ≥800℃, with incineration continuing for 2h. Select a burial pit site on high, dry ground away from water sources; the pit must be at least 1.5m deep. After burial, spread a layer of quicklime at least 0.5m thick over the surface. Spray transport vehicles with a 2% sodium hydroxide solution for disinfection, leave them for 30min, then rinse with clean water. After disinfection, leave vehicles parked at a designated location for 7 d. Check the vehicle body’s seal daily, and return it to service only after it passes reinspection.
IV. Summary
In summary, African swine fever prevention and control on small and medium-sized pig farms requires a systematic approach, adhering to the core principles of “preventing introduction from outside and preventing spread within the farm.” A multi-layered, closed-loop biosecurity protection system should be established by addressing multiple areas, including upgrading physical barriers, managing feed and drinking water safety, dynamically monitoring herd health, and implementing closed-loop control across the entire transportation chain. Production practice shows that implementing standardized disinfection, prohibiting the feeding of kitchen waste, and establishing a rapid response mechanism for abnormal pigs can substantially reduce the risk of virus introduction onto the farm. Fine-grained management measures, such as requiring transport vehicles to be registered, assigning dedicated tools to separate areas, and refining procedures for clean and contaminated zones, can effectively prevent cross-contamination within the farm. Going forward, farms should dynamically adjust the intensity of prevention and control according to their own herd size, continuously conduct hands-on biosecurity training for on-farm personnel and supervise implementation on site, and ensure that all prevention and control measures are put into practice. This will help small and medium-sized pig farms reduce disease risks and increase farming returns, while building a strong safety foundation for the sustainable development of the pig industry.