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.

For air restriction of the filter, the only answer is to have a lot of filters or install fans that perform at high static pressure. These fans are expensive to buy and operate.

For any doors where animals go in or out, air locks should be installed to protect the integrity of the air filtration system.

Positive pressure works well but can be hard on buildings by pushing warm and humid air, especially in the winter, when it gets into the walls of the building and condenses.

For negative-pressure barns, the fan covers should be left on as long as possible, and great care needs to be used to seal up sources of unfiltered air entering the building, including backdrafting through fans. Most barns are already built for negative pressure systems.

100% filtration — To ensure proper installation of filters, have a third party inspect to ensure there is a 100% seal around duct work and inlets, Feder suggests.

A number of sites have had filters damaged during installation, making it important to have the third party inspection. Education up front helps avoid someone handling and damaging the filter material.

Pre-filters should be changed or at least inspected every six months. It is best to change the pre-filters in the spring and fall after field work is completed. This also provides a good opportunity to look for air leaks or damage to the more expensive filters underneath.

Cost structure — Costs differ because of different building designs and applications of air filtration.

Partial filtration: For farms with summer tunnel ventilation and filters on ceiling inlets, cost runs $35-40/sow or boar. The estimated cost is 70-80¢/weaned pig over 10 years, including filter replacement and labor.

For the “bail out” farms, the cost really depends on what temperature the farm bails out of the filtration system.

For a wean-to-finish site, cost estimates are $1.70/pig marketed, based on filtration capacity up to 40 cfm/pig.

For 100% filtration: Darwin Reicks, DVM, has filtered five air-conditioned boar studs serviced by the Swine Vet Center. The cost of the air-conditioning system with 100% filtration is $350-$500/boar.

For barns where air flows through a cool cell, into the attic and down through ceiling inlets, cost is about $85/sow or boar and estimated to be $1.50/weaned pig over 10 years.

For barns with air flowing through ceiling inlets in the winter and tunnel ventilation in summer, cost has been $185-200/sow or boar. Extra construction cost is incurred by installing filter banks in front of each cool cell pad. More filters are needed overall as winter and summer ventilation systems have to be covered separately. Cost is estimated at $2.40/pig over 10 years.

Summary

Air filtration has quickly become the standard for boar studs in the Swine Vet Center practice, except for studs with no history of PRRS and that are located five miles or more from other pigs, says Reicks.

For sow farms, the filters need to prevent an average of 1.4 to 2.4 PRRS breaks over a 10-year period to pay for themselves, adds Feder.