Three universities are correlating tests of several odor evaluation methods. Olfactometry remains the solid standby for hog odor detection.

An estimated 200 compounds are identified as playing a role in hog odors. To pinpoint the best way to identify on-farm odor intensity, researchers at Iowa State University (ISU), North Carolina State University and Purdue University are investigating odor-testing instruments.

The three-university effort is evaluating methods with the potential to mimic human odor assessment for future development of on-site assessment tools, says Wendy Powers, assistant professor of animal science at ISU.

So far, of all the instruments tested, olfactometry remains the best bet.


The old standby for hog odor detection is human assessment using an olfactometer. Samples are collected in 10-liter Tedlar bags using a vacuum pump to create a vacuum between the rigid container and the bag. Within 24 hours of collection, a group of panelists are sequestered in a room where they sniff air samples diluted with odor-free air at three-second intervals, explains ISU animal science professor Dwaine Bundy. Concentrations are ratcheted upward until an odor detection threshold is achieved by 50% of the panelists.

Bundy started work with olfactometry in the early 1990s. ISU maintains a fully staffed olfactometry laboratory and uses a regular group of area panelists. He defends its use. “I think we have come a long way using olfactometry working with the 150-200 odorous compounds in and around livestock facilities,” he says. Despite the return to deep manure pits in hog units, identification of odor challenges has produced ventilation and other management changes for improved indoor air quality.

Now the trick is tracking hydrogen sulfide, ammonia and other hog odors downwind. To that end, Bundy has helped evaluate lagoon odor concerns in several states. A good, first-stage lagoon will be below 6,000:1 parts per million (ppm) — fresh air to odorous air — in gas detection levels.

Lagoon samples should be taken from the side opposite where the effluent enters the lagoon. Minimize variation by taking samples before lagoon loading. Recognize that bacterial counts and levels of odorous compounds will be higher in the spring when the system is turning over, he says

Bundy is exploring using an equilibrium chamber to measure gases given off right over top of the lagoon and then analyzing samples using olfactometry. “Lagoons are considered old, outdated technology. (But) it can still be a good treatment system if managed properly, loaded properly and diluted,” he reports.

As states deal with compliance issues, the demand for odor testing results is high, says Bundy. Several states perform olfactometry testing, he says.

But don't expect results for free. At ISU, grant funding of employees keeps costs down. Bundy's lab charges $75/sample, whereas some labs charge twice that much. He advises shipping two to three air samples per lagoon for best results. Round-trip shipping of odor-sampling equipment runs $40. For information on the ISU lab, contact Bundy at (515) 294-6360 or call the lab directly at (515) 294-2959.

Other Testing Methods

Olfactometry remains the best method of hog odor evaluation. Powers admits samples aren't taken often enough and/or submitted soon enough to a qualified lab to deal with a nuisance suit.

What's needed is an objective method of conducting odor evaluations on-site, she says. In that regard, improvement in instrument sensitivities will enable researchers to better characterize air samples and predict odor nuisance potential based on concentrations of specific compounds that are present.

Addressing Odor Challenges

Simply adopting better management practices corrects, with very little cost, 88% of the total odor/environmental challenges pork producers face.

That conclusion comes from data collected in the 1,550 free assessments of the On-Farm Odor/Environmental Assistance Program. The assessments are part of the first Odor Solutions Initiative project coordinated by the National Pork Producers Council (NPPC). The project involved hydrogen sulfide, ammonia and odor field measurements in five states.

Based on six-month follow-ups of the farm assessments, 49% of the standard and 55% of the high-risk challenges have been addressed, according to NPPC Research Manager Carrie Tengman. On average, it takes three to five weeks to address the challenges and from four to nine hours to implement them.

Costs have ranged from $60,000 for a secondary containment structure to an actual savings of $100/month when a new watering system was installed.

Tengman says 75% of the challenges cost less than $10 to fix.