What the smell is that

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					What the smell is that?

                                                  The majority of you probably remember a time when escaping the
Tyler Fletcher
                                              fast-paced urban life meant a peaceful drive in the countryside. The crops
Kayde Schuler                                 waving in the wind, the quiet sounds of nature, and of course, the crisp
Randall Warnock                               country air upon each breath, but that’s when it hits you. What’s that smell?
                                              Panic sets in as you reach for the window, fumbling with the latch, blaming
                                              your family and friends, not realizing that the terrible smell is caused by an
                                              agricultural livestock operation you’re passing. But which animal is mostly
                                              responsible? Is it the large-scale swine operations with their open lagoons
                                              and liquid manure spreading, or is it the dairy barns and feedlot operations
                                              and their resident cattle?
                                                  Dr. Grant Clark obtained both his undergraduate and graduate degree in
                                              agricultural engineering, and presently a research associate at the University
                                              of Alberta where he spent time working with a bioresearch engineering
                                              group. Dr. Lorraine Doepel obtained her undergraduate degree in animal
                                              science at the University of Alberta, where she then spent time working as a
                                              nutritionist in the feed industry obtaining her PhD in 1997.

                                                  We may mistakenly assume that both cows and swine in a mass
                                              agricultural production setting smell quite similar, but what causes the odor?
                                              We have receptors in our nose that tell us when something smells good or
                                              bad, which Dr. G. Clark states that the “measurement of pleasantness or
                                              unpleasantness [of odor] is called hedonic tone” and “can be different for
                                                  The difference in smell between pigs and cows is due to different
                                              microbial communities. Microorganisms can be found almost everywhere,
                                              including the animal’s digestive tract and manure. These microorganisms,                  which work in the absence of air (anaerobic), break down and degrade
                                              the manure, and as a result produce the odorous compounds that are
  Dr. G. Clark says, “…Perception depends     interpreted as smell.
  on mood, environment, or what
                                                  The type of odor causing molecule that actually gets produced is
  someone had for breakfast”. Perception
                                              influenced by differences in substrate availability in swine and cattle
  of odor is based on the ability of a
  chemical to create a response in the        manures. Dr. L. Doepel suggested that “odor is related to diet and digestive
  olfactory receptors of the nose. Upon       processes…which vary among species”. Compounds like VFAs, phenols,
  stimulation, signals inform the brain       and indoles in particular, are most closely associated with the odor we smell.
  about the properties of that particular
  odor. The number of molecules present       The.microbes.workplace
  determines if the brain will detect odor        In pigs, microbial conversion of manure is done in both the large
  and is termed odor threshold value
                                              intestine and their excrement. Dr. G. Clark states “the feces and bedding all
  (OTV). “Doubling the concentration
  doesn’t necessarily mean twice the odor”    give off volatile compounds.” Manure is mainly composed of undigested
  says Dr. G. Clark. Certain molecules have   dietary residue, bodily secretions, bacteria cells, and their metabolic remains.
  the ability to elicit a response in lower   In a swine’s large intestine and in the feces, protein that is ingested is broken
  numbers, increasing the perception of       down by microbes, and the remnants of this reaction are largely responsible
  odor, as is the case with the pig.          for the odor causing particles. Dr. G. Clark agrees, “If you feed [pigs] a lot
                                              of protein, more than they need, more sulfur-containing groups are being

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excreted.” Compounds like skatole, responsible for the unpleasant odor
in male pigs, also known as boar taint, are produced by the breakdown of
indoles. Amylase is an enzyme that is released into the pig intestine to aid in
the breakdown of starches. Since this facilitated process exists, more protein    Dr. G. Clark explains how proper
is passed through the intestine which results in more microorganisms,             storage of feces, while promoting
producing more odorous compounds.                                                 anaerobic degradation, can result
                                                                                  in the capture of biological gasses,
    Cattle, on the other hand, have a fecal composition that contains lower
                                                                                  including methane, which can then be
amounts of protein and a higher percentage of starch. “[Cattle’s] fibrous
                                                                                  harnessed as a valuable, alternative
diet… dictates a lower need for amylase in the small intestine” says Dr.          source of energy from which the only
Doepel. The microorganisms found in the cattle manure will harvest the            byproduct is CO2.
starch as their main source of food instead of protein, and as a consequence,
produce differing compounds than swine, usually considered less offensive.
    The difference in compounds produced is important because differing
molecules have different odor threshold values (OTVs) and affect the
apparent smell. Microorganisms that breakdown the protein contained in
swine manure produce branched chain VFAs and aromatic compounds with
substantially lower OTVs than molecules produced from the breakdown of
starch. In other words, since the compounds contained in swine manure
have lower OTVs, create the perception of bad odor when in lower numbers
or concentration.

          There are many ways odor can be suppressed, and these solutions
can be dependent on the animal. Management of manure plays a large role
in decreasing animal odor, for example, when spread on fields, it can be
immediately ploughed under so it does not evaporate and release ammonia.
Other alternatives like chemical treatments can be added to the feces or
used in cleaning the facilities, which will reduce the odor and limit the
growth of bacteria that can be harmful to the animals or humans. Clark
says, “Also whether you store your manure aerobically or aerobically has a
big influence on what sort of microbes grow and what kind of volatiles are
    Dr. Clark states that diet manipulation can be a means of reducing the
odor. By decreasing the crude protein intake, less protein is being excreted
leading to lower concentrations of malodorous molecules found in the
feces. Furthermore, studies have found that a barley-based diet will produce
fewer odors than sorghum-based diet due to the fermentation differences
in digestion. If blood meal is an ingredient in the swine diet, which is
high in protein, then an increase in odor emission will be a result due to
excess protein not being digested and is therefore a participant in anaerobic
    So, why does a pig smell like money? Swine produce odor molecules
that can be considered offensive in lower numbers than cattle, so in the
farmer’s defense to the critics, he replies with “well I think they smell like
money”. Cow odor is also beginning to smell like “money” because odor
emissions are becoming a greater problem of in response to encroaching
communities. Even though there is no actual legal definition determining
the amounts of odor allowed, the municipality has a say on farm expansion
and can prevent farm growth. “Europe is 15 to 20 years ahead of [Canada]
in issues of manure management”, says Clark “because they have to deal
with those issues now [odor], because of population”. All in all, as a
province, we should be looking ahead and preparing for this issue of odor
that is arising.

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