July is a special month for many families. Schools are breaking up for summer and preparations are being made for the holidays.  Our pets certainly know that something’s afoot and react accordingly as bags are packed for a few days away.  In my house, this means extreme excitement but a road trip causes stress and pleasure in equal measure.  Stress for Portia, the black Lab, who hates the car. Joy for Jessica, the terrier, who loves it!  As we near our destination, sea or farm, both dogs sniff the air as if saying, are we nearly there? (No wonder we call them our canine kids). After all, a dog’s scent is one of their many superpowers.

The Senses

I thought I would continue this mini-series of articles on the special senses (vision, hearing, touch, taste and smell). Let’s consider what the latter means to our companion animals – a dog’s scent. Touch and smell are immensely important to all of us, as a means of communication between and within species.  The canine nose has legendary abilities. As research into this area develops, we are beginning to understand what super-power dogs possess. 

Remember, when only three years ago we were all in lockdown? The search for a diagnostic test that could identify infected people was high on the priority list. Dogs have been used to sniff out several human diseases in the past. It’s not surprising, therefore, that a trial was conducted using a dog’s scent as Covid detectors.  After some training, the dogs’ success rate at identifying COVID-19-infected, people was almost as good as sophisticated scientific apparatus. They were in fact, better than the adopted lateral flow tests.  Impressively, dogs needed only one sniff to make a diagnosis. Screening a large number of people in a very short time was therefore possible.  Such a pity the blunt instrument of body temperature measurement was adopted instead. I guess some people just don’t like being sniffed, not by dogs and probably not by other humans either.

Sense of taste

We marvel at dogs’, and to a lesser extent unless medication is involved, cats’ abilities to detect different smells. I try not to dispense tablets to cats (or Poodles). No amount of disguise (cheese or not) will persuade the patient to take their daily dose. We have a handful of liquid formulations but this does little to help if they are unpalatable. This fact is seemingly lost on pharmaceutical manufacturers! Without care, liquids can be aspirated into the respiratory tract of feline and canine patients. Only small quantities of water and saline solutions are relatively harmless if aspirated. These are rarely given by mouth as intravenous fluids are much more efficient at treating dehydration.  However, occasionally we deliberately squirt a measured volume of saline into the lung or trachea. This is to analyse the residue we can suck back out, to attempt to identify the cause of lung disease.

Now, I’ve digressed a little. Dogs live in a world of smell and probably rely on that sense more than vision. Cats are more “visual”, although they can adapt to blindness, as we discussed a few months ago.  We don’t know how commonly dogs and cats lose their sense of smell and taste. Although, human experience from COVID-19 and other respiratory viral infections tells us it almost certainly happens. Cats commonly suffer from cat ‘flu’, and like us, a bunged-up nose means no smell. Only the taste sensed on the buds on our tongues (bitter, sweet, sour and salt) remains. 

The science

The fine detail of taste and smell is detected on an organ at the back of the nose, the ethmoid. This is where dogs have 300 million receptors for individual smells. What’s more, dogs and cats have another detection system, the vomeronasal organ, that detects molecules without odour. This is how a dog’s scent can determine with a sniff, the sex and mood of another. Different pheromones (air-borne hormones) are released in response to fear, excitement, aggression and pain. A relaxing pheromone has been isolated from dogs and cats and is sold commercially as plug-in diffusers or sprays. This is how it can help stressed animals feel better.

One final fascinating fact about smell is the way it can adapt to the advantage of the individual.  This allows us (humans as well as animals) to become more sensitive to certain smells while tuning out others.  As all smells are detected by receptors, which are proteins, they are all coded on our DNA.  The genes controlling these receptor proteins are prone to mutation, and favourable mutations give an advantage to the individual.  For example, imagine you were competing to find food and had a more sensitive nose for it than your competitors. You would find more, be better fed and so more likely to produce offspring. 

Evolution, we now know, is all about genetic variation arising from mutations (thanks to Mr. Darwin) in our DNA.  We humans have helped the process along by breeding dogs with the most sensitive noses, E.G. the Spaniel breeds. And that is why your sweet little Cockerpoo is a fluffy nose on legs.