Impact of different supply air and recirculating air filtration systems on stable climate, animal health, and performance of fattening pigs in a commercial pig farm

Abstract

Biosecurity is defined as the implementation of measures that reduce the risk of disease agents being introduced and/or spread. For pig production, several of these measures are routinely implemented (e.g. cleaning, disinfection, segregation). However, air as a potential vector of pathogens has long been disregarded. Filters for incoming and recirculating air were installed into an already existing ventilation plant at a fattening piggery (3,840 pigs at maximum) in Saxony, Germany. Over a period of three consecutive fattening periods, we evaluated various parameters including air quality indices, environmental and operating parameters, and pig performance. Animal data regarding respiratory diseases, presence of antibodies against influenza A viruses, PRRSV, and Actinobacillus pleuropneumoniae and lung health score at slaughter were recorded, additionally. There were no significant differences (p = 0.824) in total bacterial counts between barns with and without air filtration. Recirculating air filtration resulted in the lowest total dust concentration (0.12 mg/m3) and lung health was best in animals from the barn equipped with recirculating air filtration modules. However, there was no difference in animal performance. Antibodies against all above mentioned pathogens were detected but mostly animals were already antibody-positive at re-stocking. We demonstrated that supply air filtration as well as recirculating air filtration technique can easily be implemented in an already existing ventilation system and that recirculating air filtration resulted in enhanced lung health compared to supply air-filtered and non-filtered barns. A more prominent effect might have been obtained in a breeding facility because of the longer life span of sows and a higher biosecurity level with air filtration as an add-on measure.

Fig 1. Structure of the four barns and sampling points.

Each barn consisted of 32 pens and was accessible via two doors. Exhaust air outlets in each barn are given as circles. Slashes on both sides of the picture symbolize the fresh air inlets of barn 3 and 4. Triangles indicate the fresh air distributors of barn 1. Dust was measured at two sampling locations that were randomly selected on the day of sampling but were identical with the sampling points for air sampling. The latter sampling points (n = 6) are indicated by stars. Stars in yellow indicate sampling points for ammonia (NH₃). A (barn 1 and 3) and B (barn 2 and 4) represent the positions of the sensors for CO₂ and relative humidity. Recirculating air filter modules in barn 4 are represented by a framed X.

Fig 2. Distribution of fresh air into barn 1 and structure of the supply air filter modules of barn 1.

(2.) This figure exemplarily illustrates the air influx for one supply air filter module. Five of these modules were installed at the left long side of barn 1. Each module was connected to a corresponding ventilation pipe along with two air distributors. The direction of airflow is indicated by a blue arrow. (2.a) Supply air filter modules were composed of: A—windshield, B—prefilters and secondary compact filters, C—adiabatic cooling device. Prefilter dimensions were 592 mm (length) x 592 mm (height) x 48 mm (width). Secondary compact filters sized 592 mm x 592 mm x 292 mm (see S1 Table). The direction of airflow is indicated by a blue arrow.

Fig 3. Cross section of barn 2 demonstrating the distribution of fresh air and composition of the perforated polyurethane cassettes used for supply air filtration in barn 2.

(3.) Each filter unit consisted of a polyurethane cassette and two glass wool filters. These units (indicated in yellow) were installed into the barn attic without gaps. Fresh air entered the attic via slots underneath the roof (dark blue arrows). Air flow (indicated as multicolored arrows) was regulated by negative pressure. (3.a) Each air filter unit in the attic of barn 2 was composed of two glass wool filter mats (A, B) embedded in a perforated polyurethane cassette (C). Each mat sized 1,200 mm x 1,200 mm and had a thickness of 40 mm. The direction of airflow through each cassette is indicated by a blue arrow.

Fig 4. Cross section of a recirculating air filter module from barn 4.

Each recirculating air filter module consisted of a plastic housing equipped with a pocket air filter and a fan. The air volume flow rate was regulated via the fan. Module dimensions (mm) are specified and the direction of airflow is indicated by a blue arrow. Barn 4 was equipped with four of these modules.

Fig 5. Prevalence of antibodies against H1N1 virus in pigs kept with and without air filtration.

Fig 6. Prevalence of antibodies against H3N2 virus in pigs kept with and without air filtration.

Fig 7. Prevalence of antibodies against PRRSV in pigs kept with and without air filtration.

Fig 8. Prevalence of antibodies against APP in animals kept with and without air filtration.