This is the financial companion to the Alonso epidemiological study, a partial budget and investment analysis of air filtration in large sow herds. Reported payback was 2.1 years on a 150 dollar per sow attic filtration investment and 2.8 years on a 200 dollar per sow investment covering attic plus sidewall panels. Both assume a replacement schedule of six months for prefilters and three years for filters. The production differences underlying the model were a 4 percent higher farrowing rate on filtered farms, an additional 1.9 pigs weaned per sow per year, and a 2.3 percent lower sow mortality rate. Non filtered farms averaged a PRRS break every 1.4 years against every 7.9 years for filtered farms.
One figure from this paper is routinely inverted in secondary material and the inversion matters. The 5 dollars per pig premium for PRRS negative weaned pigs is an assumed input to the model, not a result it produced. Applied to the observed production data, it yields a mean difference of 1.70 dollars per pig in weaned pig value between filtered and non filtered farms. Writing the input as the return reverses the direction of the finding. The modelled aggregate benefit was close to 6,000 additional pigs weaned per year across the filtered farms in the model.
The authors attach conditions that travel with the payback figures and are frequently dropped. These are long term averages, not intended to apply to individual herds. They do not apply to herds at low PRRS risk, nor to herds whose broader biosecurity is less comprehensive, and the authors state that biosecurity should be first rate before filtration is considered. A payback period calculated for a herd breaking every 1.4 years does not describe a herd that breaks rarely. Note also that the figures recorded here come from a published summary of the study rather than from the full text, which is paywalled; the full paper should be read before any figure not listed here is used.