Finding the odor in livestock agriculture

AMES, Iowa -- Lingshuang Cai put her nose to the little glass cup held by a boxy machine's silver arm.

As that high-tech machine analyzed the chemistry of a dust sample taken from a poultry barn, it sent the smell of individual compounds through its arm and up to Cai's nose.

It was her job to quickly characterize each smell: Was it floral? Or maybe earthy? Buttery? Smoky? Winey? Did it smell like a taco shell?

Or -- and this is the more likely scenario in Iowa State University's Atmospheric Air Quality Laboratory -- was it piggy? Or skunky? Moldy? How about fecal? Did it smell like body odor? Or more like a sewer?

No matter the smell, Cai's expression never changed. The postdoctoral research associate just tapped her sensory judgments into a computer and waited for the next whiff. If you work in Jacek Koziel's lab at Iowa State, you get used to some odor.

Koziel, an Iowa State assistant professor of agricultural and biosystems engineering, calls the worst of the odors "needles," as in needles in the chemical haystack that is livestock odor. He's the only researcher in the country now using a $130,000 multidimensional GC-MS-O instrument to study odors from manure and barn dust.

That name is short for a Gas Chromatography-Mass Spectrometry-Olfactometry instrument, a machine that has been used for quality control in the tobacco and brewing industries. It makes it possible for researchers to make unique comparisons of chemical analysis and sensory judgments for every compound the machine detects.

Koziel, whose work is supported by Iowa State and the U.S. Department of Agriculture, thinks that instrument and the research it enables may be a key to taking some of the odor out of livestock agriculture.

The machine takes two simultaneous measurements: with its separation and spectrometry technology, it's able to identify the hundreds of compounds in livestock odor. And with its olfactometry technology, real people judge the smell of each compound.

As Koziel says, "One sniff is better than a thousand words."

Koziel and his researchers have identified a few of the key compounds that produce livestock odor: para-cresol, 4-ethyl phenol, indole, diacetyl and a few others.

The next steps in his research are to make synthetic swine odor from a few of the characteristic odor ingredients. Koziel is hoping to prove that only a few compounds are responsible for the characteristic odor. If he can do that, odor treatments can be focused on those few compounds. He'll also use his instrument to find ways to treat and eliminate the odor in manure and barn dust. And he'll use it to test several commercial treatments for livestock odor.

"We are focusing on those 'needles,' the compounds that really matter," Koziel said.

The GC-MS-O instrument will be essential for quantifying any odor differences before and after treatment. The instrument will look for changes in an odor's chemistry. And the sniff tests made possible by the instrument will allow researchers to assess whether noses detect any odor changes.

"I'm amazed at what this instrument can do," Koziel said. "It sets apart Iowa State from anybody else studying livestock odor. We can make a direct connection between a few specific gases and the livestock odor."

But that's not all his instrument can do. It's being used to identify the specific compounds that give ladybugs their foul smell. And it's being used to study whether soybean plants infested by aphids release a chemical signal that attracts ladybugs to feed on the aphids.