Dog breeds known for their special smelling abilities may not have a better sense of smell than their relatives. At least this is what a previously unpublished study by US researchers suggests. When examining the genome and the skull, they were unable to find any fundamental differences, for example between sniffer dogs and other dogs.
The group around William Murphy from Texas A
Highly valued, little understood
Dogs’ sense of smell is considered to be outstanding. This is due, among other things, to the high number of olfactory cells in the nasal mucosa, the special way of sniffing and the way smell is processed in the brain. People take advantage of the special abilities by using dogs, among other things, to search for people, drugs, explosives, detect diseases and hunt. Beagle, Bloodhound and German Wirehaired Pointer are considered to be particularly good sniffers. Greyhounds, border collies and pugs, among others, are considered particularly bad at this.
In principle, it is difficult to examine dogs’ olfactory abilities, says Juliane Bräuer. “Extremely little is known about smelling in dogs.” Bräuer is head of the dog studies research group at the Jena Max Planck Institute and conducts research into dogs’ sense of smell. For example, it is unclear what a dog actually perceives chemically when it follows a trail.
It is also difficult, for example, to use brain scans to examine the processes in the brain during smelling, says Bräuer. The animals then became stressed and started panting. But that’s a problem: “Anatomists almost agree that sniffing and panting are not possible at the same time,” says Bräuer. The number of the dog’s olfactory cells can be determined, but does not provide any reliable information about the dog’s ability to smell.
Experiments with genetic material and skulls
Murphy’s group now chose a different approach. They looked at the genomes of 30 different dog breeds and specifically looked for genes for so-called olfactory receptors. They found that dogs have fewer such functional genes compared to wolves and coyotes.
However, comparing the dogs with each other did not reveal any fundamental pattern that would explain the special smelling abilities of sniffer dogs. A look at the so-called gene expression – i.e. how strongly these genes are actually read and proteins are created based on them – did not reveal any such differences.
Murphy’s researchers also carried out measurements of the so-called lamina cribrosa on 103 skulls. This is part of the ethmoid bone, a bone at the end of the nasal cavity. The lamina cribosa is traversed by nerves that transmit olfactory information to the brain. The larger this structure is in relation to a mammal’s body size, the better the sense of smell can be.
But the researchers also found no structural differences in the lamina cribrosa between breeds known for their excellent sense of smell and other dogs. “Our results challenge breeders’ claims that olfactory traits were selected and controlled by strict reproductive controls in olfactory breeds,” the study authors write.
What do other experts say?
However, Jeffrey Schoenebeck, a dog geneticist at the University of Edinburgh, is not completely convinced in the scientific magazine “Science”. “I think there are other possibilities at play here,” he said. More investigations are needed.
“The results don’t surprise me,” says dog researcher Bräuer. After all, most dog breeds are no older than 200 years. Despite breeding, a better sense of smell does not necessarily develop in this comparatively short time. Bräuer believes that tracking dogs such as bloodhounds were not bred for special nose abilities, but rather for their motivation to smell. The differences in smelling abilities could simply be due to how much certain breeds sniff – and how often their noses are on the ground.
