For many producers located in hog-dense regions of the country, air filtration of hog buildings sounds like a good way to go, but the relatively high cost has caused some producers to be hesitant.

Filtration Systems

The Swine Vet Center headquartered at St. Peter, MN, has been a pioneer in the installation of air filtration systems for hog buildings, reports Jeff Feder, DVM. In three years, air filtration has been installed on 331 sites, with the first filters being installed in several boar studs by Darwin Reicks, DVM.

Currently, the Swine Vet Center has installed air filters in 21 boar studs, eight sow farms and in four hog finishing and research sites.

This number includes small and large farms. Five of the sow farms are 2,500 sows and the others range from 500 to 1,200 sows. All of the filtered sites are located in hog-dense southern Minnesota and northern Iowa.

More than half of the systems use 100% filtration, with others opting for a partial filtration or “bail out” system, where air is 100% filtered at lower temperatures. But as the ventilation system needs to move more air (70-80°F outside temperature), the air enters the barn unfiltered, Feder says.

The filters work by interception — particles adhere to the fibers of the filter and become trapped. Pre-filters capture large particles (dust) to extend the life of the main filter (commonly a Merv 16 or Merv 14 rating), which is designed to capture very small particles that carry pathogens such as porcine reproductive and respiratory syndrome (PRRS) virus.

Results

The goal of air filtration has never been to eliminate PRRS outbreaks totally, as there are many other routes of PRRS entry into the farm, says Reicks.

But if the incidence of aerosol transmission can be reduced or eliminated, then it offers a good return on investment, Feder emphasizes.

So far that has proven to be the case. Most of the farms that turned to air filtration had a history of PRRS breaks. To date, there have been three PRRS breaks on farms using partial filtration. All three farms were infected when the buildings were not being filtered.

One other PRRS break did occur on a 100% filtered farm, although it was discovered the filters were damaged, and there was another possible route of virus entering the farm via trucking, Feder explained in a mid-September talk at the Leman Swine Conference in St. Paul, MN.

There have been two swine influenza virus breaks on 100% filtered farms, which are believed to have originated from employees who were sick at the time, and from boars entering the farm when they were subclinically infected. There have been no breaks in herds with Mycoplasmal pneumonia, most of which are vaccinated, he adds.

Despite many calls from producers about cheaper filters, Feder says the Swine Vet Center has decided to stick with the filters produced by Camfil and marketed by Automated Production Systems, since these are the filters tested by Scott Dee, DVM, at the University of Minnesota. The Merv 16 filter (now called the L9 filter) allows 600-1,000 cfm air flow through the 24 in. × 24 in. model at 0.2 in. of static pressure. The newer L6 is another filter being used for some applications, since it allows more air through the same size filter (920 cfm at 0.2 in. static pressure).

That filter strategy will remain in force for farms with a history of PRRS or farms that have neighboring farms within two miles or a large number of farms within 3-4 miles.

A number of filtration issues are addressed below:

Partial filtration — It continues to be practiced due to the relatively high costs of installing and maintaining the large number of filters needed for maximum ventilation rates in the summer. By putting filters on the ceiling inlets and having no filtration for cool cell pads, most farms are left unfiltered for about four months of the year, Feder explains.