Why study pig odor?

Pig manure research may not smell like roses, but it's definitely not just pork in the latest federal spending bill, says one Iowa researcher


Sen. John McCain (R–Ariz.) is back at it, taking swipes at federally funded animal research projects. First he took on the grizzlies—lambasting studies to gauge whether the mighty creatures were in danger of becoming extinct and now he's peeved about pigs—or pig odor, to be precise. The former presidential candidate last week mocked a federal set-aside for pig odor research, listing it on his Twitter feed as one of the "Top 10 Porkiest Projects" allocated funding in the latest federal spending bill being debated in Congress. Sen. Tom Coburn (R–Okla.) chimed in on his own Web site that "This earmark is $1.7 million to take the stink out of manure," and pretty soon the blogosphere was snorting about liberal (and pig) waste.

Amid threats to strip the $410-billion bill of its earmarks, Democratic Iowa Sen. Tom Harkin took the floor to passionately defend his state's swine scientists. "People constantly complain, with good reason, about big farms, factory farms and their environmental impacts," he said, "so it makes good sense to fund research that addresses how people can live in our small towns and communities, and livestock producers can do the same, and coexist."

The problem with federal earmarks for scientific research is that they can be doled out based on political connections and lobbying rather than on a grant review by a panel of scientific peers. In this case, the Swine Odor and Manure Management Research Unit at the U.S. Department of Agriculture's Agricultural Research Service (ARS) in Ames, Iowa, had been stripped of funding last year by the Bush administration, and this was designed as a way to reboot the program. As Harkin put it, "This item is only included as an earmark now because the last Bush budget proposed to terminate a number of agricultural research projects in order to come in at a lower budget number, knowing full well that this needed research was likely to be restored by Congress."

But what on earth is pig odor research? To find out, we spoke with Jacek Koziel, an agricultural engineer who specializes in livestock odor at Iowa State University and who has helped the ARS team quantify odors for their experiments varying the pig's diet.

[An edited transcript of the interview follows.]

What is pig odor?
We've shown that the odor is a mixture of several hundred different gases, but there are only a handful of gases that really give it the characteristic livestock odor. To me, the top one would be p-cresol. This is a phenolic compound that we've shown is present right at the source—that is, very close to the farm—but it is also one that carries far downwind. Even when you smell it at very dilute concentrations, you would think there are some livestock nearby. Then, there are also a couple other gases that belong to volatile fatty acid groups.

We associate these smells with fecal matter or waste in general. Those aren't necessarily pleasant experiences. On the other hand, you can find similar smells in a number of foods. When the smells are associated with the visual image of cheese or wine or some other food product they aren't necessarily considered offensive.

Why is pig odor a problem?
Typically, pig odor is a localized air quality problem. We usually just have low concentrations of these potent odorous gases such as p-cresol, and those are not necessarily immediately dangerous to our health. However, odor problems are often a starting point for litigation. This is a real problem for many farmers large and small, but small operations in particular can go out of business because of this litigation. This is a real issue to many people. The need to do fundamental research on odor, on controlling odor, and on gaseous dust emissions from livestock is still there. There's no question about it.

How do you study it?
When we analyze odor samples we do it with two simultaneous methods.  The first way is a chemical analysis that allows us to identify and quantify the chemicals in the air.  The second way is to your nose to a sniff board and actually sniff each and every compound that constitutes the air sample, allowing us to determine the compound that carries the specific overall odor of any sample. That's why, in my opinion, there is no need to mitigate the hundreds of compounds in pig odor, because not all of them are responsible for that odor. There are only a handful that we need to go after: I call them the "bad guys."

How do we stop the worst components of pig odor?
My group has shown that high-energy ultraviolet light works very well in laboratory settings. We would like to move up to the commercial scale. The light induces chemical reactions that change these offensive odorous compounds into something benign or at least less smelly. This is one of those technologies that would work not only for livestock-type odors but also on different types of odors, say office or residential odors.

Or my own bathroom?
Yes, of course. There has been some research on the use of ultraviolet light in some critical environments, because UV light is also capable of inactivating airborne pathogens. You can envision this technology being used for all sorts of odors we know from daily life: bathrooms, gym lockers, crowded offices, and such. This is something that can be beneficial in many different areas, because many of these odor-causing chemicals are similar, and it doesn't matter if it's of livestock or human origin.

Are there any other techniques to reduce pig odor?
There is a more mature technology that I have also worked on in collaboration with Steven Hoff, a colleague at Iowa State. He's using biofiltration, which uses large beds of wood chips that harbor microbes. As air passes through the chips, the microbes are eating up the odorous compounds. That technology has proven to work quite well in real livestock operations.

The team at ARS also works on the nutrition side to reduce odor using additives or micronutrients. For example, the scientists will change the sulfur or nitrogen content, and they also work on tweaking the microbial flora in the gut. When you do this, however, there is always a danger of affecting animal growth, metabolism and how much meat they produce.

How did you start studying pig odor in the first place?
I did my PhD way back at the University of Texas in Austin studying sewers, so that was my introduction to smelly things. We worked on emissions of gases from sewer collection systems in pipes carrying human waste. After that, I went to Canada to work with at the University of Waterloo, and I learned this analytical technique called solid phase microextraction for sampling minute amounts of gases. That's sort of where the story with pig odors starts. Many of these odor-causing chemicals are detectable by our noses at low concentrations. The technology I learned in Canada moved me into this area in livestock. Also, growing up in Poland, I worked each summer on a small farm. My grandfather had all sorts of livestock so this all comes back to me.

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