Welfare and Behaviour
Breathing new life into research on scent in dogs
A new study shows scent hounds lack a superior genetic basis for olfactory function and confirms the association between olfactory gene degeneration and specific breeds.
Since dogs were domesticated from grey wolves over 15,000 years ago, there has been extensive variation among breeds, including differences in olfactory ability.
Brachycephalic breeds, such as Pugs and Bulldogs, have been selectively bred for their distinctive short-nosed features. As such, they are generally assumed to have impaired olfactory function and capabilities due to reduced airflow through the nasal cavity.
In contrast, scent hounds such as Beagles and Bloodhounds, have been selectively bred for their superior olfactory performance.
But what is the genetic basis of these olfactory differences?
This is what a new study, ‘Diversity in chemosensory receptor genes in dogs and wolves: Degeneration of the olfactory receptor gene receptor gene repertoire in the brachycephalic Pug’ by Inoue et al, aimed to find out - conducted as a partnership between the Waltham Petcare Science Institute and the Department of Veterinary Sciences, Faculty of Agriculture, University of Miyazaki, Japan.
Behaviour vs Biology
Several studies have examined olfactory differences between dog breeds, but with contradictory findings.
One behavioural study showed scent hounds outperform other breeds (Polgár et al., 2016). Another found Pugs ahead, but this is likely due to motivation rather than olfactory capacity (Hall et al., 2015).
And more recent genetic research suggested there is no inherent breed-based advantage (Mouton et al., 2025). Rather, that the superior olfactory performance of scent hounds likely reflects behavioural traits rather than genomic differences.
To get to the bottom of things, Inoue et al examined the variation in chemosensory receptor genes across dog breeds and between dogs and wolves, to explore a potential association with olfactory ability.
Going back to where it all began
Given the origin of dogs, this new study investigated the genetic basis of the difference between domesticated dogs and grey wolves. Single nucleotide variants (SNVs) in three chemosensory receptor gene families were analysed in 635 domestic dogs representing 121 breeds, 8 grey wolves, and 16 canine genome assemblies.
Oflactory mutations varied, but were not better in scent hounds
Compared with wolves, dogs exhibited significantly higher ratios of mutated genes, potentially as a result of domestication, which could have biological consequences.
The number of functional olfactory receptor genes varied substantially among individuals.
However, in the comparison among dog breed groups, scent hounds did not exhibit a markedly higher number of functional olfactory receptor genes than other breeds.
This concurs with previous findings that scent hounds might be chosen for scent detection tasks due to behavioural traits that make them more trainable, over olfactory capacity.
As suspected, Pugs were particularly impacted
Among breeds, Pugs had significantly fewer functional olfactory receptor genes and a higher ratio of mutated to non-mutated olfactory receptor genes than other breeds. So, not only is the functionality of the olfactory genome reduced in Pugs, but even intact olfactory genes seem to vary, affecting their sense of smell.
Compounding the issue of reduced airflow to the nasal cavity in brachycephalic breeds, these findings also link diminished olfactory ability to genetic degeneration of their olfactory receptor genes.
We're following our noses
This latest study provides valuable insights into the genetic underpinnings of chemosensory diversity among dog breeds. Through examinations at a genetic level, substantial diversity in olfactory receptor gene repertoires among individual dogs was found.
Scott McGrane, Senior Research Manager at Waltham and an author of the study, said: “Our findings help us to better understand the role of domestication and breed-specific traits in olfactory function – in particular, with regards to the Pug – and shed new light on the common perception of superior olfactory functionality in scent hounds.”
Waltham is proud to continue leading research and development into pet health, to support ongoing discovery in our efforts to build A BETTER WORLD FOR PETS™.
