Lidong has just passed, and water pipes at farms in northern China are starting to freeze.
When it comes to disinfection, many farms stick to the same routine by default: spray the same way in winter as in summer. Use the same disinfectant, at the same concentration, at the same time.
But once the temperature drops, the underlying logic changes.
One: Disinfectants really can stop working at low temperatures
The Ministry of Agriculture and Rural Affairs’ “Key Technical Points for the Prevention and Control of Swine Diseases in Autumn and Winter” states plainly that low temperatures affect the stability and solubility of disinfectants, significantly reducing their effectiveness. The China Animal Disease Prevention and Control Center’s “Key Technologies for the Prevention and Control of African Swine Fever in Winter and Spring” makes the same point.
But don’t take this to mean that “all disinfectants are useless in winter.” That’s not true.
One study tested the effectiveness of 8 disinfectants against African swine fever virus at three temperatures: 21℃, -10℃, and -20℃. The conclusion was that sodium hypochlorite, glutaraldehyde, potassium hydrogen peroxymonosulfate, caustic soda, and phenol can still achieve effective inactivation below zero; benzalkonium chloride (a quaternary ammonium compound) and acetic acid cannot withstand the cold—their effectiveness drops as the temperature falls.
So the first thing to do is check the ingredients in the container you have.
Quaternary ammonium compounds (such as benzalkonium bromide): basically, don’t count on them outdoors in winter
Glutaraldehyde, potassium peroxymonosulfate, and caustic soda: relatively cold-resistant and the mainstays in winter
Chlorine-containing products: their effectiveness drops as temperatures fall, so the concentration needs to be increased
II. The real killer isn’t the temperature—it’s freezing
This point is more important than the previous one, but hardly anyone mentions it.
The same study also says: All disinfectants freeze when left standing in sub-zero conditions. Once frozen, disinfectants cannot adequately penetrate the surfaces being disinfected, making disinfection ineffective.
In plain English: At minus ten degrees, you walk around the animal housing with a sprayer and spray. The solution comes out of the nozzle as a mist, lands on the railings, floor, and corners of the manure channels, and quickly forms a thin layer of ice. Ice is a solid; it just sits on the surface and cannot penetrate.
The gaps in the railings, the bases of the drinkers, the insides of the feed troughs, the gaps in the slatted floors, and the channel in the corner that can never be reached with a rinse—these places already need to be soaked with disinfectant to be effective. Once it freezes, it’s as good as not having sprayed at all.
On the surface, you’ve sprayed it, it’s wet, and it’s even turned white.
In reality, this round of spraying was all for nothing.
It’s not that the product is wrong; it’s that it didn’t reach its target.
For outdoor spraying in winter, choosing the right active ingredient works better than simply increasing the concentration.
Three. Why disinfecting pig housing with pigs present is not recommended in winter
An official document states: Disinfection inside pig housing with pigs present is not recommended in winter and spring.
Many people don’t understand—isn’t it supposed to be done more frequently?
Three reasons.
First, humidity. Disinfecting with pigs in the barn inevitably pushes up the humidity inside. In winter, you already cannot ventilate too much. When humidity rises, ammonia rises with it, damaging the pigs’ respiratory mucous membranes first.
Second, chilling. The pigs’ bodies get wet, especially those of piglets, and their body temperature drops quickly.
Third, at low temperatures, the disinfectant solution itself is less effective, so spraying may not do the job properly.
So for disinfection inside the barn in winter and spring, try to use the “thorough disinfection when the barn is empty” approach—as soon as possible after moving pigs and before bringing pigs in, do it thoroughly once. It works better than spraying every day with pigs in the barn.
Four. Choose medication based on temperature; the official guidance gives a clear threshold.
There’s no need to guess. The threshold provided by the China Animal Disease Prevention and Control Center is clear.
Disinfection outside the shed
· When the outdoor temperature is above -6℃: a 0.5% glutaraldehyde aqueous solution can be used
· Even at lower temperatures: use a low-temperature disinfectant, sodium dichloroisocyanurate 0.2%-0.3%, or a potassium peroxymonosulfate compound 0.2%-0.5%, with ethylene glycol and calcium chloride added to the formula for antifreeze
· Ground: apply a high-temperature flame directly
Disinfection inside the shed
· Use 0.2%-0.5% potassium peroxymonosulfate compound
· In winter and spring, disinfection inside the barn with pigs present is not recommended
Drinking water and vehicles
· Drinking water: chlorine dioxide, bleaching powder; acidifiers can be added
· Vehicles: when the outdoor temperature is below 18℃, use a low-temperature disinfectant
· The road surface can be disinfected with flame
Whitening and disinfection
· 15%-20% lime slurry + 2%-3% caustic soda, mixed to prepare a caustic lime suspension
· Alternatively, use 10% glutaraldehyde and benzalkonium bromide for foam whitening
Five. A few things that are easy to get wrong
The concentration of caustic soda needs to be increased. 2% is enough in summer; in winter, it generally needs to be raised to 5%. At low temperatures, it dissolves slowly. It’s best to dissolve it in warm water, stirring as you go. Don’t let the particles settle at the bottom of the bucket—the particles that settle there haven’t dissolved, so what gets sprayed out is plain water.
Use warm water to prepare the solution. Water at 20-30℃ dissolves it quickly and preserves its activity. But don’t use boiling water: chlorine-containing preparations decompose faster at high temperatures.
Don’t add antifreeze indiscriminately. Official recommendations include ethylene glycol and calcium chloride. However, calcium and magnesium ions increase water hardness, and hard water reduces the effectiveness of oxidizing disinfectants such as potassium peroxymonosulfate. So whether to add anything, and what to add, depends on which type of product is in your container; there’s no one-size-fits-all answer. Some sources also recommend adding 1%-3% table salt to lower the freezing point. The same principle applies: it still depends on the product.
Disinfect on sunny mornings. From 10 a.m. to 3 p.m. is the warmest window of the day. Spray in the early morning or evening, and the disinfectant may freeze before it has time to take effect.
Extend the contact time. When the risk of an outbreak is high, disinfect thoroughly 1-2 times per week, allowing each application a little longer to take effect than in summer.
Six: The disinfection pit at the entrance is the first thing to become useless in winter
The vehicle disinfection pit and personnel footbath at the entrance to the facility are the outermost line of defense for the entire site, and also the first places to become ineffective in winter.
The vehicle dip tank problem is straightforward: the water freezes. When a vehicle drives through, it only crushes the ice layer; the tires and undercarriage do not come into contact with the chemical solution at all. Some facilities think “as long as there’s water in the tank, it’s fine,” but in reality, that layer of ice is a barrier.
Caustic soda tanks have a second problem: at low temperatures, caustic soda becomes less soluble, and crystals precipitate at the bottom of the tank. The solution still looks clear on top, but its concentration has already dropped.
· Add antifreeze or 1%-3% table salt to lower the freezing point
· Measure the disinfectant concentration in the pool once a day; don’t rely on guesswork
· If it freezes over, replace the water; don’t break the ice and make do
· In extremely cold regions, route vehicles through a drying room, or use a flame to provide supplementary disinfection of the tires and undercarriage
A footbath for personnel is even simpler: one pool of water used all day, with dozens of people walking in and out, will have lost its effectiveness long ago. In winter, it is recommended to switch to changing footwear and using a spray, or to change the disinfectant solution frequently. Don’t expect one pool of water to last all day.
Completely clearing out the empty pens is more practical than spraying the pigs every day.
Seven, Bringing Supplies In: Let Cold Items Warm Up First
This is unique to winter; in summer, it is almost never a concern.
Supplies brought in from outdoors during winter have cold surfaces. When disinfectant is sprayed on them, the solution’s temperature drops, reducing its effectiveness. That means the disinfection is being done with a partially ineffective solution.
The official recommendation is:
· Disinfect the materials after they have returned to room temperature
· Drying preferred: 60-70℃, 30 minutes
· For items that need soaking: use warm water at around 25°C and soak completely for more than 30 minutes
· Let stand: let stand at 25°C or above for 10 days; let bagged feed stand at 20-25°C for 14 days; bulk feed silo for 7-14 days
Pay attention to the words “completely submerged.” Supplies floating on the surface, with part of them above the water, don’t count as disinfected.
Eight. Clean the floor before disinfecting.
This applies in every season, but it matters even more in winter.
Organic matter such as manure, feed residue, and blood-contaminated water directly consumes disinfectant. This is especially true of chlorine-based products: as soon as they come into contact with organic matter, they get “used up,” and the effective concentration sprayed onto a dirty floor may be only a fraction of what it was.
The correct order is: manure removal → rinsing → drying → disinfection → drying again.
In winter, the challenge is the “drying” step. Temperatures are low, and you can’t risk opening the ventilation too wide. Disinfecting while the pens are still wet is like diluting the disinfectant solution all over again.
If conditions allow, leave the empty pen for a day after rinsing and let the surface dry completely before applying the treatment. If not, at least sweep away any standing water on the floor.
Foam coverage can extend the time the treatment solution stays in place; this step is even more worthwhile in winter.
Nine. After disinfection, how can you tell whether it worked?
Don't just assume it's done because it was sprayed.
Ask yourself four things:
· Did it freeze when sprayed?
· Have you covered the hard-to-reach areas, such as the gaps between cages, the bases of the drinkers, the inside of the feed troughs, and the manure channels?
· Is the concentration sufficient? Are you still using the summer caustic soda concentration of 2%?
· Is the contact time long enough? Rinsing it off half an hour after spraying is as good as not doing it at all.
If you’re unsure, disinfect with a coat of whitewash. The limewash goes on white; wherever it isn’t white is where you missed. This is the simplest and most straightforward way to check.
The challenge of winter disinfection has never been whether to disinfect, but whether the disinfection actually reaches everywhere.
The disinfectant is right, the concentration is sufficient, and the contact time is long enough—but once ice forms or a blind spot is missed, all that work is wasted.