This study followed a commercial fattening piggery in Saxony holding up to 3,840 pigs and compared supply air filtration, recirculating air filtration and unfiltered barns. Recirculating air filtration produced the lowest total dust concentration, at 0.12 milligrams per cubic metre, and the best lung health scores. There was no significant difference in total bacterial counts between barns with and without filtration, with a p value of 0.824, and no difference in animal performance.
The null results are as informative as the positive ones. Filtration reduced dust and was associated with better lung health, and it did not measurably change total bacterial load or growth performance in this herd over this period. Total bacterial count is a broad measure that aggregates organisms of every origin, including those generated inside the building by the animals themselves, which a supply air filter does not address. This is the field companion to the laboratory work published by Wenke and colleagues in 2017, where filter prototypes were tested against specific organisms under controlled airflow.
Figures for PM1, PM2.5 and coliform reduction that appear attached to this paper in secondary reviews were not verified against the paper itself and are not repeated here. What can be relied upon is the dust concentration and the lung health finding. For a producer, the honest reading is that supply air filtration in this setting delivered a measurable air quality and respiratory health benefit without producing a performance gain, and that the case for filtration on a commercial site rests principally on preventing pathogen introduction rather than on production response.