Allowing a truck or trailer time to dry after it’s been washed and disinfected isn’t a luxury, it’s a necessity.
The value of this important final biosecurity step has been reinforced by recent research, says swine veterinarian Robert Thompson.
“Through personal experience in inspecting trailers, allowing time for appropriate drying does not always happen,” he says. And there’s more to the task than simply letting the trailer sit for a while. For example, an improper slope at the parking site may allow water to pool, thereby increasing the time needed for complete drying.
“During the winter months it’s even more difficult to get the drying effect unless the trailer can be left in a heated bay,” notes Thompson. But the reality of the situation is that trailers are often left in a cold environment, allowing remaining water to freeze up inside.
He points out that some viruses — specifically, TGE — have been shown to survive in a frozen state for a prolonged period.
So what do you do? Proper cleaning is the first and basic step, after that, contact time and environmental temperature are key for disinfectants to perform properly. Exposure time, type and concentration of organisms, concentration and type of disinfectant, temperature and pH all enter into the equation, determining the success or failure to inactivate the microorganisms.
“Empirical rules suggest inactivation time decreases by a factor of 2 to 3 for each 10°C temperature increase,” says Thompson. He notes that the infectivity of porcine reproductive and respiratory syndrome virus persists for 6 to 20 minutes at 56°C.
Increasingly veterinarians are emphasizing the importance of the trailer-drying process for biosecurity reasons. One process that is being examined is trailer pasteurization. This idea originated from the poultry industry where buildings are heated to eliminate certain environmental pathogens, notes Thompson.
Early devices to dry trailers were made from grain-dryer heating elements. Initially two heating elements were mounted on steel I-beams at trailer height. To decrease the amount of time to dry and reach a critical temperature throughout the trailers, additional heating units were added, says Thompson. More sophisticated models are available now; PIC is trying out a prototype and studying the results.
Commercial pasteurization units are becoming available. One patent-pending unit allows the warmed air to recycle. The target temperature is 165°F for 10 minutes. Estimated fuel usage is 8 gallons of propane for a 35- to 45-minute heating cycle. Estimated cost for fan heaters, hook-up, frames, gas lines, gravel and temperature sensors total $21,417.
“This heating process will better assure the consistent biosecurity status of trailers following cleaning and disinfection,” says Thompson. The largest benefit will come from reducing the downtime of drying, and the temptation to cheat the process, which only compromises biosecurity.