Winter pig diseases are often difficult to control not because of the pathogens themselves, but because the environment first gives pathogens a “key.” Low temperatures extend the time viruses can survive. Ventilation is sacrificed to retain heat, allowing ammonia and dust to accumulate continuously inside the pig house. At the same time, pigs use a large amount of energy to keep warm, leaving fewer resources for the immune system. For every 5℃ drop in temperature, the incidence of respiratory diseases increases by approximately 30%; when the day–night temperature difference exceeds 8℃, cortisol levels can rise by 40%—60%, directly suppressing immune function. The pathogens have not become stronger out of nowhere; the environment has first torn a hole in the pigs’ defenses.
The logic of winter prevention and control, therefore, is not to “treat every disease,” but to first manage the environment—the master switch—and then target the critical control point for each disease.
I. The Causes of Disease in Winter: Three Gaps Compound
Pitfall one: The zero-sum trade-off between ventilation and insulation. Sealing windows to retain heat is instinctive, but when ammonia concentration exceeds 20 ppm, respiratory cilia begin to shed and become paralyzed, giving Mycoplasma and pleuropneumonia a chance to take hold; when humidity exceeds 75%, the survival time of viruses such as PRRSV increases significantly. “It is better for the temperature to be slightly lower than to compromise fresh air.” If the air does not sting the eyes, irritate the nose, or feel damp and stuffy after entering the barn, that is a more reliable indicator than a thermometer.
Pitfall two: Low temperatures make disinfection “less effective.” When the outdoor temperature is below -6°C, the effectiveness of conventional disinfectants drops sharply. Switch to low-temperature disinfectants such as sodium dichloroisocyanurate or potassium peroxymonosulfate compound. In farrowing and nursery barns with high indoor humidity, prioritize dry-powder disinfection: it can kill pathogens while absorbing moisture and reducing humidity, avoiding the increased chill in the barn caused by liquid disinfection.
Pitfall three: Susceptibility windows differ across pig groups at different stages. Suckling piglets are most vulnerable to enteric viruses, nursery pigs to mixed respiratory infections, and breeding pigs require attention to both reproductive disorders and limb and hoof problems. Using the same program for all pig groups will inevitably miss the mark for some and go too far for others.
II. Key points for diagnosis and treatment by disease: address the “critical points” first, then discuss medication
Respiratory syndrome: Mycoplasma is the “key pathogen”
In winter, ammonia and dust levels rise inside the barn, making mixed infections involving PRRS, PCV, Mycoplasma, APP, and Glaesserella parasuis highly likely. Mycoplasma first damages the ciliary barrier, allowing other pathogens to penetrate deeper into the lungs. Therefore, control should start with Mycoplasma, rather than waiting until coughing and labored breathing become severe before using the strongest antibiotics.
Key signs: Mycoplasma is mainly associated with persistent dry coughing, most noticeable at night, early in the morning, and around feeding time. Body temperature is usually normal, and feed intake is largely unaffected, but average daily gain and feed conversion ratio gradually worsen. APP, by contrast, is an acute killer: onset is rapid and deaths occur quickly. Bloody froth from the mouth or nose is a strong warning sign, and cases often occur in clusters after temperature fluctuations or regrouping stress.
Medication strategy: When only mild coughing is present and feed intake has not yet been affected, mix tylvalosin and doxycycline into the feed and use continuously for 7 days, focusing on suppressing Mycoplasma and PRRS. It is recommended to start treatment 10 days before the seasonal transition. Once coughing and labored breathing become pronounced and feed intake declines, switch to tilmicosin and florfenicol to cover bacterial secondary infections such as APP and Glaesserella parasuis. Suppress the “key pathogen” first, then address secondary infections; reversing the order will greatly reduce treatment efficacy.
Viral diarrhea: A sow’s colostrum is the piglets’ “vaccine”
PED, TGE, and rotavirus can survive well in low-temperature environments and pose a far greater threat to newborn piglets than to adult pigs. The key to prevention and control is not the piglets with diarrhea, but the sows’ immunity before farrowing and the quality of their colostrum.
Immunization schedule: Immunizing sows once each at 40 days and 20 days before farrowing is the basic framework. A more detailed approach is to give three booster shots at 40, 25, and 10 days before farrowing, ensuring that secretory IgA in the colostrum peaks at farrowing. For PEDV live attenuated vaccines, frequent blanket vaccination is not recommended. One live vaccine dose per year is sufficient; use inactivated vaccines to reinforce immunity at other times. Frequent shedding may instead cause sporadic cases to persist on the farm.
Colostrum is more important than vaccines: Piglets have no antibodies in their bodies at birth, and all their protection comes from the first few mouthfuls of colostrum after birth. If a sow does not produce enough milk, piglets may still develop diarrhea no matter how thoroughly they have been vaccinated. During a diarrhea outbreak, promptly administer oral rehydration salts to piglets to prevent dehydration. Thoroughly disinfecting, drying, and warming the farrowing room is more lifesaving than blindly adding antibiotics.
Foot-and-mouth disease and African swine fever: the “bottom-line diseases” of winter
The foot-and-mouth disease virus is extremely stable at low temperatures, and winter is traditionally a high-risk season. If it enters a farm, production across the entire farm comes to a halt. Vaccine immunization coverage and the antibody qualification rate are the only reliable lines of defense. Before winter, the entire herd should be checked to ensure that every animal requiring vaccination is vaccinated.
The risk of African swine fever also rises in winter. The virus “thrives in the cold and fears heat; thrives in dampness and fears dryness,” and low temperatures extend its survival time in the environment. The clinical signs of low-virulence strains are often atypical. Repeated reductions in feed intake among sows, a rising proportion of abortions, and sporadic deaths warrant greater vigilance than typical high fever and hemorrhage. If these signs are detected, the right action is to isolate the animals immediately, collect samples, and submit them for testing—not to first treat them with medication for an ordinary disease and observe.
Three. Systematic prevention and control: put resources where the “leverage” is greatest
First, prioritize the environment over medication. Maintain the localized temperature in the piglet activity area of the farrowing room at 30—32℃, and the temperature in the nursery at 22—25℃, lowering it gradually each week; keep the temperature in the finishing barn at no less than 16℃. Keep the day–night temperature difference within 5℃, and temperature changes per hour to no more than 2℃. Seal gaps that cause drafts with foam sealant or burlap sacks. Add deflectors at air inlets so cold air first mixes with the warmer air above, avoiding direct airflow onto the pigs. Use timed air circulation with low-volume negative-pressure ventilation. Concentrate air exchange during the midday high-temperature window, and maintain the minimum ventilation rate at night. Keep ammonia below 15ppm at all times.
Second, the “timing” of vaccination matters more than the “number of times.” Check core vaccines for foot-and-mouth disease, classical swine fever, diarrhea, and other conditions, and administer any necessary booster vaccinations before winter. Monitor antibody levels after vaccination and promptly revaccinate if they are inadequate; do not assume that “vaccinated” means “protected.” PED vaccination should be precisely timed around the pre-farrowing period, rather than applied with equal intensity throughout the year.
Third, use medication “precisely,” not as blanket coverage. A common winter mistake is to “keep medication in the feed long-term out of fear of disease.” Limit preventive medication to clearly defined stress periods, such as regrouping, cold snaps, or feed changes, and use it short-term for 3—5 days. For treatment, first identify the infection site and pathogen type: for intestinal infections, select medication that reaches high concentrations in the intestine; for systemic infections, select medication with strong tissue penetration. Do not use antibiotics as a substitute for reducing disease pressure through environmental and management measures.
Summary
The prevention and diagnosis and treatment of common winter diseases can be summed up in three sentences: the environment is the first line of defense, immunity is about precise targeting, and medication is for plugging gaps, not as a safety net.
For respiratory diseases, first target Mycoplasma, the “key pathogen”; for diarrhea, focus on sows’ colostrum; and for foot-and-mouth disease and African swine fever, maintain the baseline of immunity and monitoring. Get these four “non-medical” measures right—ventilation, temperature differences, disinfection, and humidity—and many winter diseases will never reach the point where “treatment” is needed. In winter, success in pig farming is not about how full the medicine cabinet is, but about having fewer gaps in the environment and fewer mismatches in immunity. (Source: Zhang Weiguang)