A four-year University of Minnesota research trial found that air filtration was 100% effective in blocking porcine reproductive and respiratory syndrome (PRRS) virus from entering a model of a swine production region.

As a result of this research work, air filtration has been rapidly applied to commercial swine production.

But to determine the actual effectiveness of blocking the introduction of PRRS with air filtration, a pilot study was conducted of new infections in large breeding herds in swine-dense regions of northern Iowa and southern Minnesota. In this field trial, three veterinary clinics — Pipestone Veterinary Clinic of Minnesota, Fairmont (MN) Veterinary Clinic and the Swine Vet Center, St. Peter, MN — and the University of Minnesota tested thousands of sows. The findings were reported at the August George Young Swine Conference held in South Sioux City, NE

Pitted against each other were sows housed in filtered barns vs. sows housed in non-filtered facilities located in northwest Iowa and southwest Minnesota, says Pipestone Veterinary Clinic’s Bryan Myers, DVM, of Independence, IA.

To qualify for the study, herds had to have at least 2,400 sows and be surrounded by four or more growing pig sites within a radius of about three miles. The candidate herds also must  have experienced a minimum of three external PRRS infections over the past four years despite the use of industry standard biosecurity practices, he says.

Standard filtration systems were installed in attics and/or as a filter bank using validated efficient filters, Myers says,

Following installation of filtration systems, PRRS status was monitored across all of the herds on a monthly basis, assessing clinical evidence of PRRS and reviewing production data.

Blood samples were collected from breeding herds and tested for the presence of PRRS virus using polymerase chain reaction (PCR).

The study was conducted from Sept. 1, 2008 to Jan. 15, 2012, with the 38 herds evenly divided between filtered and non-filtered operations.

 

Results

During the course of the study, there were eight new PRRS virus introductions in the filtered herds and 89 new introductions in non-filtered herds. All of the infected herds exhibited clinical signs of PRRS, confirmed by samples submitted to state diagnostic laboratories, Myers says.

The median time between PRRS infections averaged 11 months for non-filtered farms vs. 30 months for filtered farms.

“Owners who even had a (single) break after filtration were ecstatic compared to the numerous breaks they experienced before filtration,” he points out.

“The implementation of air filtration significantly reduced the occurrence of new PRRS virus infections in breeding herds. The odds for a new PRRS virus infection in breeding herds before air filtration was nearly eight times greater than the odds after air filtration was initiated,” Myers notes.

Tougher Challenge

“We are sending out huge plumes of virus into the environment, and farms are getting exposed to a lot more virus in the last few years compared to 5-10 years ago,” Myers says.

He says newer PRRS strains appear to be more virulent than the older strains of the virus, and it’s not uncommon to find multiple strains circulating simultaneously in the air space around a farm site.

Filter Decisions

Myers lists five factors to consider when deciding whether to take the air filtration plunge:

1.  Location of the farm

2.  Pig density in the area

3.  Frequency of breaks

4.  Severity of breaks

5.  Pig flow

“At the Pipestone Veterinary Clinic, we deal with some commingled finishing pig flows. All pigs need to be PRRS negative, as mixing PRRS-positive pigs and PRRS-negative pigs will most likely result in a severe disease outbreak,” he stresses.

Older buildings and multiple buildings on a site also represent challenges to biosecurity that may hinder the effectiveness of an air filtration system, he adds.

Ensure that all biosecurity practices have been upgraded before installing a filtration system.

Myers says the initial cost to filter a sow operation averages $300/sow, plus an ongoing cost of $1.00/weaned pig to maintain the filters.