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return to Farmers
Independent Weekly
April
24 , 2003
by Qiang Zhang, Department of Biosystems Engineering |
Human
noses beat machines at detecting hog odour
Raising
pigs doesn’t have to mean raising a stink! As Manitoba’s
hog industry has grown in recent years, community concern
over the smell of hogs has been major impediment to industry
expansion.
There
is continuing research to cut the smell and much of it is
proving successful. But since odour lies in the nose of the
smeller, how can scientists actually measure the good against
the smelly? Right now, most researchers use machines but new
data from southern Manitoba and Alberta proves trained people
can actually do a better job!
Odour
from hog operations is a complex mixture of many different
odourous compounds resulting mainly from the anaerobic decomposition
of hog manure. Nearly 200 compounds have been identified in
livestock odours. Human perception of odour depends on the
concentration of each compound and the combination of these
compounds as well. As both the concentration and the combination
of these compounds are highly variable, measuring odour presents
a serious challenge to researchers and regulatory agencies.
Currently,
dynamic-dilution olfactometers are considered to be a standard
method of odour measurement. This method, however, is not
suitable for sampling odour downwind from odour sources in
the field. Could human sniffers do the job as well or better?
I and my colleague John Feddes, animal scientist at the University
of Alberta, wanted to find out.
We
knew that St. Croix Sensory Inc. in Stillwater, MN, had developed
a sniffing method by training and certifying human sniffers
as Nasal Rangers™ to use n-butanol as odour reference
scales to rank odour. We designed a study to investigate the
relationship between odour intensity assessed by Nasal Rangersand
odour concentration measured with olfactometers. The study,
initiated and completed in 2001, was supported by the Manitoba
Livestock Manure Management Initiative Inc. and Alberta Agriculture,
Food and Rural Development.
In
this study, Nasal Rangers were trained to use an eight-point
odour intensity referencing scale, prepared as mixtures of
eight different concentrations of n-butanol and water solutions
from 120 to 15500 ppm. To take an odour measurement, the Nasal
Ranger put on a carbon filtered air mask to clear his/her
nose for about two minutes and sniffed the air (odour) for
about 30 seconds. The Nasal Ranger then assigned an intensity
level (0-8) to the odour by “matching” the odour
intensity with one of the levels (concentrations) of n-butanol
solutions. While Nasal Rangers were sniffing, odour samples
were also collected in Tedlar™ bags for olfactometer
analysis. Four sites were selected for this study - two hog
operations in southern Manitoba and two hog operations in
central Alberta.
We
found that when the Nasal Ranger detected high odour intensity
in the field, the odour concentration measured with olfactometers
from the bagged samples changed little. In other words, the
odour samples taken in Tedlar bags could not capture instantaneous
bursts of strong odour in the field. On the other hand, odour
intensity of bagged samples measured by Nasal Rangers in the
laboratory correlated well with the odour concentration measured
with olfactometers. This means that sniffing by Nasal Rangers
was is a reliable method for odour measurement.
Training
human sniffers (Nasal Rangers) is relatively straightforward
and relatively low cost. Therefore, this method could potentially
be adopted by regulatory agencies at the provincial level
or even at the municipal level as an odour monitoring/accessing
tool.
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