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Tracking a Dog’s Keen Sense of
Smell
All
dogs have a sense of smell far superior to that of humans. This
amazing ability is useful to the dog in many ways — from
communicating with other dogs to finding the perfect spot for
rolling. Not nearly as important for survival as it once was, a
dog’s sense of smell has long been used to track food for himself
and humans.
Today, people use dogs in a variety of roles due
to their superior olfactory ability. Dogs have invaluable roles with
search and rescue teams, in identifying contraband, tracking game
for hunting, and keeping tabs on endangered species. Recently, dogs
have even been trained to identify bladder cancer in
humans.
“The act of scent detection is a very complicated
metabolic function,” says Robert Gillette, D.V.M., M.S.E., director
of the Sports Medicine Program at Auburn University College of
Veterinary Medicine. “It involves odor reception, recognition and
location. All of these are necessary for dogs to use their special
scent abilities.”
How
the Canine Nose Works
A number of things make a dog’s
scenting ability superior, most notably anatomy. The shape and
length of a dog’s muzzle, as well as his habit of sniffing, is
uniquely suited to extreme smelling ability. Some dogs have longer
ears, which may also play a role in helping to funnel scent
molecules into the nose.
Starting at the nostrils, their
shape is unique to allow expiration out of the sides of the nose so
that fewer scent molecules in the air or on the ground are
disturbed. The actual act of sniffing heightens a dog’s scenting
ability by disrupting the normal breathing pattern and allowing
scent molecules to stay in the nasal passages longer.
The
dog’s nasal cavity, like a human’s, is divided into two parts by the
septum, which is formed from bone and cartilage. The nasal cavity
contains a number of turbinate or cartilagelike bones. Those closest
to the nostrils, called nares, warm and moisten incoming air.
Further back in the cavity, the turbinate bones are covered by
olfactory mucosa, a thick spongy membrane.
The mucosa
consists of millions of microscopic cilia, or thin, hairlike
structures sprouting into the passages. The olfactory mucosa and
cilia also help keep dogs healthy by trapping dirt and other foreign
objects so they don’t enter into the respiratory system. The size of
the olfactory mucosa varies greatly within breeds, and may be one of
the primary factors that certain breeds are able to smell better
than others. Dogs may have as few as seven or as many as 60 square
inches of olfactory mucosa, while humans only have about one-half to
one square inch.
Scented molecules are trapped in the mucus
and processed by odor-detecting cells found on the tips of the
cilia. Estimates of the number of these sensory cells range from
about 125 million in the Dachshund to 300 million in the Bloodhound.
Humans have far fewer, with estimates ranging from just five to 10
million of these specialized, odor-sensing
cells.
Jacobson’s
Organ
The vomeronasal organ (VNO), also called
Jacobson’s organ, is an especially sensitive part of a dog’s sense
of smell. Found on the roof of the mouth, the VNO is comprised of a
pair of small, cigar-shaped, fluid-filled sacs. These sacs are
filled with receptor cells that are sensitive to chemicals that may
not have an odor, such as pheromones.
Dogs access the organ
by licking or snapping the air, drawing chemicals into the mouth.
All mammals have a VNO, but it was thought to be inactive in humans
since prehistoric times. Newer research shows that it still
functions in humans but isn’t as fine-tuned as the VNO in a
dog.
Once the receptor cells in the nose pick up scent
molecules, messages are fired off to the brain. “Once this
information reaches the brain, the brain has to identify it as a
scent and then determine its significance,” Gillette
says.
While anatomical structure heightens a dog’s ability to
smell, what happens in the brain may be even more important, he
says. “It’s here that dogs are able to discriminate between smells
and components of smells, which can be further enhanced through
training,” Gillette says.
A classic study of dogs’ olfactory
capabilities showed that dogs could reliably discriminate members of
a single family, including siblings and even fraternal
twins.1 A trained dog can retrieve the one stick handled
by his owner from a pile of 20 or 30. In other tests, dogs trained
to detect a certain odor were able to identify the scent even when
presented with a complex blend of scents.
Olfactory Roles for Dogs
Search and rescue (SAR) work is one of the most widely
recognized and admired uses for dogs’ phenomenal sense of smell.
According to the National Association for Search and Research,
requirements for the SAR dog include trainability, agility,
endurance and the ability to get along with other dogs and people.
SAR dogs are usually larger working and sporting breeds, such as
German Shepherd Dogs, Dobermans, Rottweilers, Golden Retrievers,
Giant Schnauzers and Labrador Retrievers.
Similar to search
and rescue, tracking sports mimic the skills required for SAR by
testing a dog’s ability to follow a human scent and locate articles.
The American Kennel Club’s first tracking competition was held in
1936 as part of obedience competition. In 1947, tracking became a
separate sanctioned event.
Since that time, title
designations have evolved signifying levels of accomplishment. These
include: Tracking Dog (TD); Tracking Dog Excellent (TDX); Variable
Surface Tracking (VST), which tests a dog on urban settings; and
Champion Tracker (CT), a special designation for a dog that has
earned all three tracking titles.
The U.S. government uses dogs
extensively in detection work searching for bombs, drugs and other
contraband. One of the most recognized efforts is the Beagle Brigade
used by the U.S. Department of Agriculture at major airports to
sniff the luggage of travelers for prohibited fruits, plants and
meats. The program seizes an average of about 75,000 prohibited
agricultural products each year. After two years’ experience,
Beagles hit an average success rate of 90 percent, according to the
agriculture department.
In September 2004, the British
Medical Journal published the results of a study demonstrating that
dogs can smell cancer in humans. Seven dogs, all pets, were trained
to distinguish urine of people with bladder cancer from urine of
people who were healthy and people who have diseases. The dogs were
tested numerous times with seven urine samples in each test, one of
which was from a person with bladder cancer.
As a group, the
dogs correctly identified the urine from the bladder cancer patients
22 out of 54 times, reflecting a 41-percent success rate. Two of the
dogs, both Cocker Spaniels, had the best records with 56-percent
accuracy.
Interestingly, all of the dogs repeatedly selected
one of the control specimens from a person who was found through
testing to be free of bladder cancer. The person underwent
additional testing and was found to have a kidney
carcinoma.
Olfactory
Senses & Hunting
Dogs have long been favored
partners of hunters. Field trials mimic the skills of hunting
similar to how tracking mimics SAR work. Field trials vary based on
the hunting specialty of the breed. For instance, Basset Hounds,
Beagles and Dachshunds follow scents of rabbits, while Coonhounds
track raccoons and Pointers and Spaniels air-scent
birds.
“I’ve been hunting with Coonhounds for about 50
years,” says Purina Consultant Harold Kirkes of Farris, Okla. In 1998, he owned the
high-scoring English Coonhound in the Purina Outstanding Coonhound
race. In competition Nite Hunts, he enjoys hunting with three and
four dog casts, which he says can result in the hounds tracking and
treeing multiple raccoons in a short period of time.
Despite
having been bred to hunt, not all Coonhounds are great hunters from
the start, Kirkes says. “Some dogs aren’t that good at tracking,
while some are naturals. With those dogs you expose them to the
elements, and they’re off,” he says. Kirkes likes to let his older,
more experienced dogs train the younger ones. “Once they’re trained,
I let them do their job,” he says.
Sean Derrig, owner of
Erin Kennels in Tiskilwa, Ill., has champion English
Pointers that compete in horseback field trials, but he also has
Beagles and Coonhounds for hunting rabbits and raccoons. He
appreciates the special talents of his dogs. “It amazes me to see a
dog running down a fence line using the wind to his or her
advantage, ‘swap ends,’ head high taking in the scent of a covey of
quail that may be 10 to 20 feet away,” he says. “Or, that Beagles
will be tracking a hot, fresh trail, head 10 feet in the wrong
direction, turn around and boom, be right back on
it.”
Maintaining
Olfactory Senses
A number of things can impede a
dog’s ability to detect scent, Gillette says. These include issues
related to health, nasal structure, mental capacity, nutrition and
conditioning.
“A dog’s excitement to work can have a negative
effect on his detection abilities,” Gillette says. “The anticipation
of work will initially decrease the scenting ability because the
excitement overrides the thought process of detection. After the dog
calms down, his scenting ability will improve. After time though,
fatigue can set in, which diverts energy away from scenting and can
impair the thought process related to scent.”
Medical issues
also can alter a dog’s ability to smell and can reduce his
conditioning level, Gillette says. Some health problems that are
commonly seen in athletic and working dogs are tick-transmitted
illnesses, such as ehrlichiosis and Rocky Mountain spotted fever, as
well as fungal diseases, kidney or bladder
infections.
Gillette recommends a veterinary examination two
to three times a year for active dogs. A general health examination,
lameness examination, and blood, fecal and urine testing should be
included. The blood workup should include a complete blood count, a
blood chemistry profile, with thyroid level and tick titers.
“Athletic and working dogs are more affected by low-grade metabolic
issues than the normal pet population,” he explains.
When
talking about his hunting hounds and field trial dogs, Derrig
believes, “Most dogs have good noses, but some dogs just use them
much better than others.”
1 Case LP. The Dog: Its
Behavior, Nutrition and Health. (Ames, Iowa: Iowa State University
Press, 1999.) p.50.
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Friends We Make Along the Way
Purina’s Bob West, Director of the Sporting Dog Group, is passionate
about sporting dogs and people who love them. In 40 years as a
professional trainer, West has put more than 100 titles on dogs. Here
he shares lessons learned while competing and gives advice about
getting into the game.
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start as a professional trainer by first working as an obedience
trainer. Today, she has trained 20 AKC Master Hunter Labradors, earned
a spot on the Women’s Challenge Trophy, and become an inspiration for
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the Article>
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and field tests in which they are judged against a demanding standard.
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the Article>
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