A dog's nose is maybe the most distinguishing feature of the face. Flat-nosed dogs such as bulldogs, pugs and Pekingese look nothing like long-nosed German shepherds, bloodhounds or collies. So it's natural to wonder whether the long nose serves any particular purpose and whether scent hounds -- dogs who can follow the scent of an animal, such as the basset hound, beagle, bloodhound and coonhound -- really do have a better sense of smell than their flat-nosed counterparts.
The back of a dog's nasal cavity contains a membrane called olfactory mucosa. The olfactory mucosa membrane helps trap scents. The bigger the nose the bigger the membrane. The membrane's size varies among breeds, from 7 square inches to 60. Once the scent molecules are trapped by the olfactory mucosa, smell- or scent-detecting cells process the scent molecules and send the information to the brain.
The bigger the dog's nose, the more smell-detecting cells it contains. The best noses for smell-detecting activity are long, wide noses because they can hold the most scent-detecting cells. The size of the dog doesn't matter as much as the size of the nose. A beagle, for example, has just as many smell-detecting cells as a German shepherd, according to Stanley Coren, a professor at the University of British Columbia and the author of dog books, in "Psychology Today."
The top scent-smelling dog is the bloodhound, a breed with a large and wide nose. That breed has 300 million scent-detecting cells, which is why bloodhounds have traditionally been used as hunting companions and to track humans both in search-and-rescue operations and to catch criminals. Some courts accept evidence from bloodhound trails, according to the American Bloodhound Club's website. Besides the long, wide nose that helps the bloodhound pick up scents easily, the long neck allows the breed to follow a scent with the nose to the ground without becoming fatigued in the shoulders. A bloodhound's long ears, or the long ears of any scent hound, likely help funnel smells to the nose, according to Purina's website.
The bloodhound has the most scent-detecting cells. His nose might not be the longest of all the breeds, but it is the most massive; it's long and wide. Combine that with the droopy ears that sometimes act to direct odors to the nose during tracking and trailing and with the neck that allows the bloodhound to remain with his nose to the ground for a long time, and you have a smelling machine. Compare the bloodhound with the German shepherd, who has 225 million scent-detecting cells, and the dachshund, with 125 million. People have only 5 million of them. Even a flat-nosed dog has a better sense of smell than humans and likely has close to 100 million scent-detecting cells.
Although some breeds have been bred to hunt, such as coonhounds; many are not naturals, said Harold Kirkes, a Purina consultant. Some dogs need training to track using their noses. Sean Derring, a dog kennel owner in Illinois, summed up the phenomenon well on the Purina website when he said, "Most dogs have good noses, but some dogs just use them much better than others."
- Purina: Scenthounds
- Psychology Today: Do Some Dog Breeds Have Better Noses and Scent Discrimination Than Others?
- The American Bloodhound Club: History of the Bloodhound
- Purina Pro Plan: Tracking a Dog's Keen Sense of Smell
- The American Bloodhound Club: What Do They Look Like?
- The Whole Dog Journal: The Canine Sense of Smell
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