One of the most interesting and useful things about canines is their incredible sense of smell. Scientists have determined that a canine’s sense of smell is between 10,000 and 100,000 times better than ours. This is the reason canines are so commonly used to locate cadavers, participate in search and rescue, and work alongside us as hunting and tracking dogs. There are even cancer sensing dogs, and their olfactory system is put to work in additional activities that involve smell, such as detection dogs for security duty (including at airports and train stations).
So, what exactly goes into all of this? We spoke with Bloodhound Breeder and Trainer Judy Braun, who has had several dogs succeed in tracking and mantrailing using their innate and sophisticated olfactory system. Dogs like Judy’s can detect and follow scents that are imperceptible to humans.
“Canine noses can have over 300 million olfactory receptors, which are responsible for detecting and interpreting scent molecules,” Judy explains. “This is in contrast to the 5 million olfactory receptors that humans have. The olfactory receptors are located in a specialized area of the canine’s nasal cavity known as the olfactory epithelium, which is coated with mucus.”
When a dog detects a scent, the odorant molecules are being drawn up into their noses as they engage in what we call “sniffing.”
“The scent molecules become trapped in the layer of mucus, which contains enzymes that break down the odorant molecules into more manageable molecules. They then bind with receptors, which cover the olfactory epithelium,” Judy continues. “Olfactory receptors then detect the scent molecules and send signals to the brain, where they are processed and interpreted (making the scent profile or scent picture).”
The olfactory bulb in the brain of a canine is also larger than a human’s, meaning it can process and interpret scent information much better than ours can. But what dogs are able to accomplish when it comes to scent is even more impressive than that. It may seem simple at first glance, but the shape of a dog’s nose actually has something to do with why they’re so much better at picking up and tracking scents than we are.
“The canine’s nose is long and narrow, which allows them to effectively sniff the ground and pick up scent molecules,” Judy says. “The nostrils are located on the sides of the nose, which allow the canine to differentiate between scents coming from different directions.” Short-nosed dogs, however, like Pugs, have also demonstrated their incredible scenting abilities.
The aforementioned olfactory system possessed by canines is incredibly sensitive, with the ability to detect scents at a concentration as small as a few parts per trillion. This is especially important to people like Judy, who look to create and train dogs that can succeed in mantrailing.
“This is because it allows a canine to detect even the smallest amount of scent left behind by the quarry,” notes Judy. Dogs also have an internal structure located at the roof of their mouth called the vomeronasal organ (VNO), which is also known as the Jacobson organ. “When a dog encounters a particularly interesting scent, it will often open its mouth, inhale the scent, or touch (not lap) it with its tongue, allowing the odorants to come in contact with the vomeronasal organ,” Judy explains. “This is particularly important when detecting pheromones.”
There’s even more that goes into dogs using their heightened sense of smell. Here’s a look at how scents can be dispersed and how it affects the dogs, according to Judy.
Precipitation, such as rain or snow, can also affect the scent trail. Scent molecules can be washed away or diluted by the precipitation, making it more challenging for the canine to track the trail.
Water is a polar molecule and, as such, attracts odorant molecules. This will come into play around ponds, rivers, creeks, and any body of water as well as around trees. Hardwoods contain less moisture and almost repel odorant molecules in a chimney effect, whereas softwoods contain more moisture and attract scent molecules in a masking effect.
Water vapor in the air, or humidity, is another factor that affects the dog’s ability to track a scent trail. When the air is humid, scent molecules remain closer to the ground, making the scent trail more defined and easier for a dog to track. On the other hand, when the air is dry, scent molecules disperse more easily, making the scent trail less distinct and more difficult to follow. In addition to affecting the behavior of scent molecules, humidity can also affect a canine’s ability to detect and process (heavenly) scents.
