THE SNIFF TEST

Mark Newton-Clarke MAVetMB PhD MRCVS,

Clarke Veterinary Surgeons

July is a special month for many families, schools breaking up for summer and preparations 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 and joy for Jessica the terrier who loves it. As we near our destination, sea or farm, both dogs sniff the air and look at us as if say, ‘Are we nearly there?’ No wonder we call them our canine kids.

I thought I would continue this mini-series of articles on the special senses (vision, hearing, touch, taste and smell) by considering what the latter means to our companion animals. Clearly, 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 and as research into this area develops, we are beginning to understand what a super-power dogs possess. Remember just three years ago we were all in lock-down, subjected to daily doses of gloom as SARS-Covid-19 ravaged society? The search for a diagnostic test that could identify infected people was high on the priority list and as dogs have been used to sniff out several human diseases in the past, it’s not surprising a trial was conducted using dogs as Covid detectors. It’s also not surprising that after some training, the dogs’ success rate at identifying Covid infected people was almost as good as sophisticated scientific apparatus and better than the adopted lateral flow tests. What’s more, the dogs needed only one sniff to make a diagnosis so screening a large number of people in a very short time was possible. Such a pity the blunt instrument of body temperature measurement was adopted instead but I guess some people just don’t like being sniffed, not by dogs and probably not by other humans either.

I continually 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 as no amount of disguise in sardines or cream cheese 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, a fact seemingly lost on pharmaceutical manufacturers. Liquids that are not taken readily by our canine and feline patients can also result in aspiration into the respiratory tract if care is not taken in their administration. Only water and saline solutions are relatively harmless, in small quantities, if aspirated and these are rarely given by mouth as intra-venous fluids are much more efficient at treating dehydration. However, occasionally we deliberately squirt a measured volume of saline into the lung or trachea to analyse the residue we can suck back out, in an 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 really 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 and only the taste sensed on the buds on our tongues (bitter, sweet, sour and salt) remains. The fine detail of taste and smell is detected on an organ at the back of the nose, the ethmoid, 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 one dog can determine at a sniff the sex and mood of another, as 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 that 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, if you were competing to find food and had a more sensitive nose for it than your competitors, you will 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 selecting dogs with the most sensitive noses, the spaniel breeds, and bred from the best. And that is why your sweet little cockerpoo is a fluffy nose on legs.