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by Brian Holmes (C)2014 - How Does My Dog Smell?
for the latest scientific information


Sadly, because we humans depend far more on sight and sound to communicate and understand what is happening around us, we have very little understanding of how important a dog's sense of smell is to their everyday life and mental well being. This is because our sense of smell is very poor in comparison to that of a dog - humans have approximately 5 million scent receptors in their nose while the average dog has over 200 million, and working dogs such as scent hounds can have between 230 to 300 million. Another way of describing how amazing a dog's sense of smell is to use the analogy of a dog being able to find a single grain of sand on a 10m square patch of a beach!




When a dog takes a short deep sniff (rather than normal breathing) moisture on the surface of a dog's nose helps to capture scent molecules in the air and dissolve them. These molecules then come into contact with the olfactory membranes deep inside the dog's nose which send nerve impulses to the olfactory centre of the brain (which is forty times larger in ratio to the olfactory centre of a human brain). These nasal membranes cover the nose's wafer-thin turbinate bones and have convoluted folds to ensure that the minutest amount of scent can be captured within them and assessed accurately.


Dogs also have the ability to detect sex scent as the molecules in the air come in contact with the roof of their mouths and trigger the vomeronasal organ situated there. This organ transmits information directly to the limbic system of the brain which controls the dog's emotional behaviour.


Swedish scientists have recently discovered that dogs have heat (ie. infrared) detectors alongside the scent receptors in their nasal cavity. This enables hunting dogs to sense a prey's body heat when the dog is downwind of it.


Scientist have proved that a dog can detect one part in a million of scent in distilled water. This ability to detect and differentiate scents has resulted in dogs being used throughout the world for detection and rescue, not just for hunting.

Dogs detect scent molecules in two different ways - sniffing the air for traces of a particular scent, or from sniffing the ground or objects with scent on. Some dogs seem to have a preference for air scenting or ground scenting but all dogs are capable of doing both to some degree or other.


AIR SCENT (see also under Behaviour/Understanding your dog)
Air scent occurs when a disturbance is made by whatever has recently passed through the air (eg. an animal, human, or a toy that has been thrown for the dog to retrieve - see Find It). It is affected by atmospheric conditions - temperature, humidity, wind speed and direction - and the time that has elapsed since the air was disturbed. Air scent disappears more quickly than ground scent.

Examples -

  • Your dog can detect the scent of any treats or toys that you are carrying in your pockets, hands, bumbag etc. As soon as you begin your walk, your dog will know exactly what you have hidden around your person for its reward for "good behaviour". This is why so many dogs do not come back when called - they already know what the handler has to offer them and there is no element of surprise or anticipation for the dog. This is why our treat boxes are so effective - the dog cannot detect what type of different foods the handler is carrying until the lid is taken off. I always enjoy watching a dog's look of surprise and sudden interest when a treat box lid is opened and it suddenly detects all the different and enticing food scents that suddenly appear in the air around the handler. Don't underestimate the power of a pleasant surprise on a dog's sense of smell when you are training a dog - it can be an extremely effective photo!
  • Another misunderstood aspect of the sensitivity dogs have to air scent is when dogs bark "for no apparent reason". What is actually happening is that the dog is detecting the scent of other dogs (and/or humans) that are passing its territory, even when the doors and windows are tightly closed or when the "intruder" is a long distance away. I have plenty of instances where dogs that are in houses, sheds or kennels detect the scent of passers by in the wind and begin barking a territorial warning, or bark to communicate as the dog feels lonely and stressed. An amazing example of this is when I am walking my dogs on the Malvern Hills and we come to a valley where houses are built at the very bottom and are a great distance from the high path that we walk on. As soon as we turn into this part of the Hills a household of dogs that live at the bottom of the valley begin howling and barking (what the neighbours think I can't imagine as there is no way that they can see us walking on the path above!) and stop as soon as we have walked downwind of the property.
  • Dogs use scent a great deal when compiling environmental photos of enjoyable or threatening events to store in their long-term memory. One of the most obvious examples of this is when driving your dog to the seaside, or agility shows, that it has visited in the past. The dog can detect the same environmental scents in the air as it did when it last visited the location and this photo triggers anticipation and excited behaviour from the dog.


"Ground scent" is the term that is used when dogs are following a track along the ground.

  • DISTURBANCE - Scent molecules are left on the ground by an animal or human disturbing the surface as it walked across it. For instance, blades of grass would be crushed, earth disturbed by the weight of the human or animal, fallen leaves moved or crushed, twigs and stalks snapped and bruised.
  • ANIMAL "DUST" - Animals leave minute fragments of skin, feather or fur (and pheromone scents) as they move across the ground and a dog can detect and recognise the subtle differences between not only species but specific animals as it follows this trail of dust particles.
  • HUMAN "DUST" - Humans not only leave fragments of dead skin and hair behind them, they also leave particles from their clothing, footwear, and the manmade scents that they are wearing such as perfume or deodorant. Dogs are also able to detect the emotional state of the human it is tracking by the scent of the pheromones in the air or on the ground.

Tuna Tracking mimics ground scenting by leaving a very unusual but highly stimulating ground scent which the dog has usually not come across before. The dog soon realises that this exciting scent game only happens when their handler is around and so it builds a strong bond with the handler and the dog is far less likely to wander off and "read the newspaper".

Walking your dog off-lead explains how scent, sight and sound have an effect on when and why dogs come back to their owners after they have run off.


One of the biggest and most enjoyable benefits of watching your dog working with its nose is that you begin to understand and learn about your dog's body language and relate the same signals to other aspects of the dog's life.


For instance, dogs often hold their tail in a particular way when they are really concentrating. I have noticed this with one of my collies who loves to play all sorts of different nose games with me - when he is really focused he raises his tail very high and curves it over his back. I recognised the same body language when I was teaching him to go over a dogwalk in agility and realised that he was concentrating just as hard on learning this new "game" as he was when following a scent. I recognised his concentration and commitment and gave him plenty of praise and reward for working so hard.

Other changes in body language that you may see in your dog when using its sense of smell are -

  • Whole body rigid and still as the dog sniffs the scent either on the ground or in the air.
  • Mouth open to catch more scent molecules in the roof of its mouth
  • Licking its nose to keep it moist so that it can dissolve more scent molecules
  • Suddenly standing still, and perhaps raising a paw as if in mid-stride. This behaviour is encouraged and bred into pointing and setting dogs that have to detect prey with their noses then stand perfectly still and rigid, pointing in the direction of the prey's hiding place. They have been bred to stand still for long periods of time until the hunter arrives and drives the prey out with flushing dogs so that he can see and shoot the prey. This is the reason why so many setting and pointing dogs get "lost" on walks in the countryside - they catch the scent of a nearby animal and stand and "point" or "set" until their handler comes to release them. Unfortunately the handler may not be able to see the dog's body language and will shout and whistle to try to get the dog's attention and return to them, unaware of the dog's need to be released from its working stance.


Dogs need and enjoy using their brains to detect, analyse and assess scents in their environment. However, they are unable to concentrate properly if they are distracted by movements or sounds from nearby. Therefore, resist the temptation to talk to your dog in any way until the dog has found the end of the track, object or finished the exercise. If you praise your dog by saying "good boy" while it is still working, it will stop sniffing the ground as these words are usually said as a release command to finish a training exercise. Also try to keep your body movements to a minimum when your dog is deep in concentration.


Although dogs sense of smell is phenomenal, it is not infallible. There are certain things that can have an effect on the scent itself, or on the dogs nose.

  • Weather conditions - dry, wet, cold, warm, snow, rain, fog, mist, sun, wind
  • The age of the track - ie. the time between when the track was set and when the dog was asked to find and follow it
  • Ground cover - straw stubble is very sharp and unpleasant against a dog's nose; it is far harder for a dog to find a follow a track over long grass rather than short grass; twigs, leaves and branches can be distracting for some dogs when they are learning scent games.
  • "Shouting" in scent terms - newly dug or ploughed earth and cut grass both give off very strong scents that can overpower a dog's sense of smell; animal or human tracks either crossing or on top of the track (ie don't do subtle scent games near paths or busy thoroughfares).
  • Overpowering strong manmade scents - eg. petrol, fresh paint, tar, room or air fresheners, scented candles, essential oils, household cleaning products etc - are another "shouting" problem for dogs. Some dogs can be especially effected by strong scents, such as dogs in kennels with strong disinfectant, creosote or timber preservatives in their everyday environment. Meanwhile some dogs have very strong reactions to certain scents (lavender for instance is supposed to be a calming essential oil, but it can cause sudden anger for some individuals!) So many of these strong smells can hinder a dog's sense of smell (for an hour or more) and result in them being unable to use their noses effectively.
  • Pollen can aggravate the membranes in a dog's nose, while citronella is a skin irritant and can be particularly painful when inhaled into the dog's sensitive nose. Also beware of products containing Tea Tree Oil as there have been cases of dogs showing adverse reactions due to the quality and strength of this highly overused natural oil.


Dogs are able to cope if they lose their sense of taste, hearing or sight but find life extremely difficult to cope with if their sense of smell is impaired or lost - it is the equivalent of a human becoming deaf, dumb and blind and having to live alone in modern society.

One of my dogs wears a plastic "basket" type muzzle when walking off-lead, yet he has no problems at all sniffing around and following any scent or track that he comes across. He wears the muzzle because when he is excited from chasing rabbits or squirrels, his adrenaline levels rise sharply and he occasionally chases after cyclists or joggers that happen to be passing at the "wrong time or place". With the muzzle on I have no worries about him causing any harm to anyone (or rabbit or squirrel!) and can allow him the freedom to exercise his body and mind in a safe and controlled manner.



From the moment that a puppy is born the first sense it uses is scent as it blindly searches for its mother's teat and begins to suckle. This is the puppy's first Environmental Photo - the smell of the milk and its mother, the taste of the milk in its mouth, and the heat and physical closeness of its mother are all perceived as very rewarding and pleasant and will be remembered for the rest of the dog's life. Over the next couple of days the puppy will depend solely on its sense of smell to explore its surroundings and these early "photos" can have a profound effect on the puppy's development and how it will perceive its world for the rest of its life.

With this in mind, an old towel with the breeder's scent on it (and later on the pup's prospective new owner's scent) can be left in the whelping box so that the puppy builds up strong and happy associations ("photos") with the scent and will feel at ease when they meet the humans. However, make sure that the towel does not have a strong chemical scent on it that will "pollute" the human's scent that you are trying to introduce to the puppy.


Also be aware that too much exposure to too many scents can confuse and stress puppies and so I recommend the introduction of ONLY ONE ORGANIC TYPE SCENT A DAY that the puppy will eventually come in contact with as it grows older. For instance, the saturated scent of one of the following can be put on the tip of a cotton bud and held in front of the young puppy's nostrils. Make sure that the puppy does not come in contact with the cotton bud (there may be harmful germs present) and that the puppy is not held or restrained - otherwise it may build up unpleasant associations with the scent and affect the puppy's behaviour when it comes across it later on in life. Instead, the breeder should stroke the puppy in a calm and pleasant manner so that the puppy feels confident and at ease with the new and exciting scent.

  • Human scent* - Get the human to rub the cotton bud in their hand and then seal the cotton bud in an air tight container by itself until it is presented to the very young puppy (ie Seal & Keep).
  • Foods* - Rub the tip of cotton bud on the puppy food that it will eventually be given when it is older the Seal & Keep. Also introduce it to the interesting smells of foods that it may be given as treats when it is older by rubbing the tip of the cotton bud on a bit of cheese, cooked meat etc.
  • Compost - Push the cotton bud tip into your compost heap so that it can smell the "exciting" scents of rotting vegetation then Seal & Keep.
  • Fresh or dried grass - Rub the cotton bud tip on your lawn, or on hay or straw, then Seal & Keep.
  • Seaweed - If you have access to the seaside, rub a cotton bud tip on a piece of seaweed then Seal & Keep.
  • Flowers* - Using only one type of flower at a time, rub the tip on the flower head so that it picks up the scent, then Seal & Keep.
  • Other dogs* - Rub the cotton bud along the dog's fur so that it picks up traces of the dog's scent. You can also gently rub it on the dog's paw (where it is able to sweat). Seal & Keep.
  • Rubber, Leather, Wool, or other materials* that it's toys will be made out of. Seal & Keep.
  • Raw fish - Another exciting smell that will stimulate the young puppy's sense of smell. Rub the tip of the cotton bud on the fish then Seal & Keep until required.

* Only one variety of the scent on the cotton bud at a time.


When the puppy is weaned and introduced to its new home more interesting scents should be left on a variety of different articles, once again one scent at a time. For instance, put an interesting new scent on -

  • Pieces of different textures of material
  • Various surfaces in the garden
  • Rubbed into raggits or grabbits that the handler plays with the puppy - but do not leave these training aids unattended as they will soon be chewed and destroyed!

The puppy can then be introduced to various Mind Games to help it develop and explore further its amazing sense of smell . This can also be done with dogs of any age or background.

There are many amazing benefits of introducing new and interesting scents to dogs rather than just letting it make its own entertainment by "Reading the Newspaper". The dog -

  • Builds up a strong bond with the handler who provides such interesting scents and games for the dog to do while the handler is around. This is particularly true for dogs that have very little mental stimulation in their everyday lives, and those dogs that have become Lodgers.
  • Will make a conscious effort to lower its levels of stress and adrenaline in order to concentrate on the scents that it is trying to analyse. This is one of the most effective ways of "de-stressing" dogs which are displaying "unwanted behavioural problems" and are in fact symptoms of stress.
  • Gradually builds up the mental capacity to concentrate for longer periods of time. This ability can then have a profound effect on the dog's more traditional training (eg. staying in one position until it hears or sees your next command, doing a chain of exercises such as obedience or agility).
  • Finds scent work helps to stimulate its mind and fulfill its working instincts. Many breeds and types of dogs have been bred for hundreds of generations to do particular work for humans - see Instincts. Most of these dogs are now kept as pets and have very little opportunity to fulfill their original working drives. However, a Mind Game session once or twice a week where the dog is using its brain and senses to their utmost limits not only tires the dog far more than a hour or more strenuous exercise, it feels as if it has used these working instincts and can really rest and relax until it is asked to "work" again later in the week.


Some breeds, such as scent hounds, have been specifically bred to have very high nose sensitivity and these breeds often have the distinctive appearance of having either -

  • Big droopy (and usually drooling!) jowls hanging down from their upper lip
  • Extra folds of skin around the face and/or neck which fall towards the ground as the dog lowers its head
  • Long pendulous ears that touch the ground when the dog is sniffing.

The jowls, ears and folds of skin act like an umbrella around the dogs amazingly sensitive nose, enabling the dog to confine the scent molecules on the ground without the wind blowing them away while their ultra efficient wet noses detect the slightest scent so that it can be analysed and assessed by its brain.


Tracking dogs, such as the Bloodhound or the Elkhound, have been bred to have phenomenal powers of mental and physical stamina so that they can concentrate on following one particular scent over long distances without being distracted by any other scents that they may detect while tracking. Depending on weather conditions and the terrain that they are working on, these dogs are able to follow tracks that are sometimes over 24 hours old and can differentiate between old tracks and those that have been made more recently.


On the other hand, flushing dogs are bred NOT to concentrate on following just one scent but to move quickly and erratically in the undergrowth and drive the prey out for the hunter to shoot. I use the phrase "Spot Scenting" to describe the brief and random thought processes that these dogs have for any one particular scent, or use the analogy of a butterfly moving haphazardly from one flower head to another in its search for nectar.


Although it is fairly obvious that dogs use body language and sound to communicate with one another, we often misunderstand how important scent is for communication between dogs and, to a lesser extent, other animals. Scent is a major factor in a dog's social development, not only as a puppy but throughout its life.

Dogs communicate by leaving their scent in six different ways -

  • Urine*
    Some dogs have got "weeing" off to a fine art! My 11 year old dog has always had amazing bladder control and will store up vast quantities of urine for over 12 hours so that he can urinate at various strategic places on his fairly long walks off-lead on the Malvern Hills (eg. gateposts, specific trees or rocks, lamp posts etc). I only realised how much his bladder could hold when I took him to a training venue one morning and he realised that he was not going for a walk and proceeded to empty his bladder for 2 or 3 minutes so that he could concentrate on "working" with me in the training area.
    Our young bitch, on the other hand, has a crafty trick of drinking from puddles and then urinating in them so that she leaves a "very big scent message" for the other dogs to sniff (but not necessarily drink from!).
  • Faeces*
    Yes, dog "poo" is smelly, disgusting and a health hazard but every living creature has to get rid of its waste products somehow or other! However, dogs also use their faeces to act as another source of leaving their scent in the environment. Some dogs seem to enjoy analysing what the other dog has eaten by sniffing their faeces and can sometimes progress to enjoying the smell and taste so much that they eat the faeces.

* If a dog is unable to relieve itself outside its own house and garden, it is often a sign of its insecurity and anxiety as to its rank and status in the "dog world of scent " that it is walked in. I am always pleased to see a dog relieve itself when it comes to Dog-Games training for the first (and even subsequent) time as the dog feels relaxed and comfortable enough in the environment to leave a "message" for the other dogs to find (even though we clear the poo away, of course, after each dog has been trained!). This scent "message" also acts as a Rewarding Environmental Photo so that the dog recognises that it has been relaxed and happy in the training area the next time it comes, whether it be a week or even two or three weeks between visits.


  • Anal glands
    These are situated either side of the dog's anus and produce a very smelly secretion with the faeces. This strong scent is another way for a dog to leave a "message" on the environment.
  • Scratching the ground
    Some dogs scratch the ground after relieving themselves (with grass and leaves flying everywhere - and sometimes faeces as well!). Scratching and disturbing the earth, grass and other vegetation makes the "scent message" all the more noticeable and intriguing for any other dogs that come along afterwards.
  • Rubbing themselves against something
    Just as cats rub themselves against objects to leave their scent behind, dogs sometimes rub themselves against boundaries, humans, furniture etc in order to leave their scent on them. They may also do this in order to rub and massage themselves as well - dogs love to be touched!
  • Pheromones
    These are external chemical messengers that enable dogs to detect various emotional states of not only dogs but humans as well (see Human Emotions such as Fear (and Happiness)). Pheromones help dogs to detect another dog's gender and sexual activity (eg. if a bitch ready to mate), levels of stress, fears or aggression, as well as calmness, relief, being relaxed etc. There is a very moving example of how pheromones effected two different dogs in very different ways in Our Dogs section of the website.

Because a dog's sense of smell is so acute, it is able to differentiate another dog's

  • Identity - is it friend, enemy, a newcomer or prey? If the dog considers the other dog as a friend and part of its pack, it will overmark the scent with its own so that both scents merge and become a new "identity" to any other dogs that come across the scent.
  • Age (ie. puppy, juvenile, adult, or veteran) and therefore its rank or status not only in its "pack" but in the neighbourhood it lives or exercises in. More assertive bitches (and dogs) mark more than submissive ones.
  • Gender - male or female, neutered or entire.
  • Emotional state and levels of stress - depressed, anxious, overexcited, happy, contented and relaxed. These are all detected through pheromones (see above).
  • Health
  • Sexual arrousement
  • What its diet consists of.

I like to compare this sniffing to humans reading - hence my expression "reading the newspaper" - and the scents that they leave behind "writing on the newspaper"! It is a vital part of a dog's life that it is able to "read" and "write" as it enables the dog to communicate with other dogs without having to physically be there. What dogs find so rewarding and satisfying about "reading the newspaper" is that every dog's "scent message" will be subtly different from the ones it did the day before. They enjoy the mental stimulation of reanalysing the scents to search for these subtle changes.


A classic example of dogs "reading the newspaper" is when I return home after training and/or being near to other dogs. My three dogs take great delight and concentration in sniffing me (especially my hands and trousers) to find out everything they can about the dogs I came in contact or close proximity too.

Many dogs are also apprehensive about coming too close to another dog and enjoy communicating by sniffing the other dog's scent "messages" and leaving their own "message" for the other dog to smell later on. This "reading the newspaper" is particularly useful when introducing dogs to a new neighbourhood or training venue (see Where and When), as the dogs can learn a great deal about each other by sniffing each other's markings before actually meeting and displaying body language to each other.


Dogs can become very frustrated and/or lonely because of the huge gulf of misunderstandings and lack of communication between themselves and their human "pack" (see Lodgers). For instance -

  • The dog's calming signals are often misunderstood or ignored
  • It may be given sufficient physical exercise while being walked on a lead but not be allowed to sniff the environment and thereby stimulate its brain and fulfill its working instincts

Therefore, detecting and analysing scents of other dogs can be even more important to these dogs who are starved of communication and welcome any type of contact with their own species.

Dogs also leave their scent to mark the boundaries of their territory. This warns other dogs to respect these boundaries and not to trespass. This is often backed up with barking if dogs come too close to their territory


Dogs are also able to detect the human's pheromones caused by stress, excitement, anger, anxiety or apprehension. This is why dogs become fearful or aggressive when they are close to humans that are nervous (often because the human has been bitten or frightened by a dog in the past). The dog recognises the scent of fear on the human and thinks that they are going to attack the dog, so it attacks first in "self defense". This is also true for dogs that are fearful of other dogs - they become "victims" and are attacked by other dogs because they can detect the fearful dog's pheromones either on the ground or in the air and believe that it will attack them.


One sad example of a dog picking up a human's apprehension was a dog I knew that became fearful and withdrawn whenever the handler walked down steep slopes while walking the dogs. The dog picked up the handler's fear of falling over and became worried as well, even though it did not understand why the situation was fearful.


On the other hand, dogs can also be positively affected by the scent of pheromones given off by emotions such as calmness, happiness and contentment. If humans feel relaxed and calm, their scent triggers similar behaviours in their dogs as well.


Dogs will also sniff the ground to diffuse a stressful situation (see Calming Signals). The dog itself may be stressed and so it sniffs the ground in an attempt to find a pleasant experience or photo that will distract it and help lower its stress levels. In other instances, the dog may pick up the stress pheromones in a human and try to calm the human down by displaying this calming signal.

A human equivalent of this displacement activity is idly drawing or doodling as we think, twisting our hair in our fingers, rattling keys or coins in our pocket, or constantly playing with komboloi (Greek worry beads).


Because dogs have far more sensitive noses than their rather limited taste buds, the scent of their food is far more important than its taste. This is why dog food manufacturers sell so much processed dog food, as cooked meat smells far more appetising and palatable than raw meat (although cooked meat has far less nutritional value than raw and therefore has to have artificial additives added to the pet food).


A practical example of how dogs love to use their sense of smell is the use of Treat Boxes in training. Rather than giving a treat to the dog in your hand, a tiny tasty treat is placed in a sealed treat box so that the dog cannot detect what treats the handler has on their person. When it is time to reward the dog the handler bends down and holds the treat box so that the dog can "steal" the tasty treat out of the box, licking and sniffing it inside and out just to make sure that the very last molecule has been licked from it. Even though the treat is gone in an instant, the whole process of sniffing and licking the box is very exciting, stimulating and rewarding to the dog and is a very strong motivator. Make sure that you have a wide assortment of scents of treats to choose from when placing the tiny morsel of food in the treat box - after all if the same type of food is given each time as a reward, there is little or no anticipation for the dog - it already knows what the treat is going to be as the handler gave it to them last time....


In conclusion if you find that your dog is sniffing a lot you may have to ask yourself these questions -

  • Is the dog bored and therefore it uses its only opportunity to stimulate its brain and fulfill its working instincts while out on walks? Try Mind Games.
  • Has it become a lodger because there is a lack of communication between what the dog's expectations and requirements are and that of the humans? See Lodgers to find out how to overcome this problem.
  • Is it sniffing the ground in an attempt to resolve the stress and conflict it perceives around it? See Calming Signals.


HOW DOES MY DOG SMELL? by Brian Holmes


Perhaps the first thing to say when looking at how dogs use their noses is that we don't know the full story yet of what happens between sniffing and smelling and any resulting behaviours or responses that come from that information being processed in the brain.


Despite a widespread view of the incredible olfactory abilities of dogs, and an increasing usage of dogs in scent-related working environments over the last few decades, there has not actually been a huge amount of research to identify the limits of a dog's olfactory abilities. Although research efforts are reportedly increasing it leaves us with some substantial gaps in knowledge at this point in time.


A lot work on animal perception and processing of information taken in via the various senses has been done on mammals in general, rather than dogs specifically, so some leeway on potential differences between species should also be acknowledged.


Similarly, with the research that has been done we should note that there hasn't been a common approach on experimental methodologies for quantifying these capabilities so results have differed and might well be considered in more of a range than in absolute terms.


The 'science' behind how a dog smells also spans a number of different academic disciplines so the aim here is to take an overview of what we know about dogs and their sense of smell and walk on our tip toes across disciplines to try and get down a little bit deeper to gain an understanding of what we do know and how that is relevant to SPRINKLES (TM).


So, overall, we will cover some things that we do know and some things that we think we know about how our dogs smell.


Dogs live in an olfactory world. Their primary means of perceiving the world around them is through taking in smells from the environment through their nose.

These smells are used to detect prey or other foods via foraging (and is used in conjunction with taste for food selection), noticing hazards in the environment (anything from a fire to another predator), identification of others (e.g. family members), selection of mates, and smell is also important in communication. A whole chemical world of 'Pee-mail' and 'NoseBook' is out there invisible to us and is an area which we are only beginning to understand.


So how good are the olfactory capabilities of dogs? Researchers have found their ability to detect an odour was sensitive to one part per billion against a more concentrated distracting odour. Other research put their sensitivity to some odours at one to two parts per trillion.


Those kinds of numbers are hard to understand so consider some of the applications we have put dog's noses to as a way of understanding how incredible they are compared to humans.


Drug and explosive detection are well-known applications but there are also biomedical applications such as cancer detection for various types of cancers; seizure warning for epileptics and both detection and warning with diabetes. Other applications have included wildlife conservation whether that be detecting ribbon snakes in their natural habitat or determining if a bee hive is over a fungal or parasitic mite threshold, either of which could lead to a colony collapse. As well as cadaver dogs that search for dead bodies (or evidence of the presence of dead bodies) there are specialist cadaver dogs that can locate dead bodies underwater. That dogs can detect, discriminate and identify these scents is truly amazing.


It is an obvious thought that the basis of a dog's olfactory abilities compared to humans is structural i.e. they have a big nose compared to us! The simple truth is that they are designed for smell in a way our noses are not.


Clearly we can run into some breed differences so, generally speaking, dogs take in smells through their nostrils into a large nasal cavity which is lined with a mucosa in which a large number of olfactory receptor neurones sit on the olfactory epithelium (along with other cell types). Information gathered here via the receptor neurones is sent up to the olfactory bulb (part of the limbic system and the first sub-system involved in processing information sent from the olfactory system) towards various other structures in the brain.


For perspective the olfactory epithelium is approximately 3cm²-5cm² in humans but 75cm²-170cm² in dogs. Humans have somewhere in the region of 20-40 million receptor neurones to put to work on incoming smells but dogs have hundreds of millions running into billions of the same receptor neurones. Dogs also have a functioning Vomeronasal (or Jacobson's) Organ which serves particular olfactory functions relating to uptake of pheromones and a role in reproductive behaviour so mammals have two separate parts to their olfactory system where humans have one.


There is also a genetic role in olfactory ability with the number of actively functional genes within the olfactory gene repertoire significantly higher in dogs compared to humans. The number of olfactory receptor related genes is similar in dogs and humans but a much higher proportion of those genes are non-functional in humans - evidence that evolutionary adaptation has moved humans away from using their sense of smell as much as maybe we once did while domestic dogs still have well over 80% of the olfactory repertoire functional.


Even with nature providing a structure designed to smell the contribution of sniffing should not be underestimated as part of the overall olfactory capability as it facilitates taking in smells from the environment and transporting them through the nasal structures.


So, structurally, dogs are very well equipped for olfactory perception of their environment. But what happens after an odour is inhaled and how does that relate to SPRINKLES (TM)?


How olfactory information is processed, where in the brain it is specifically processed and what results on behaviour that processing then has are still developing areas.


Work has been done in other mammals such as mice although more work is likely to be done on dogs directly as non-invasive methods progress. While we do know a reasonable amount about where information is processed in general in the brain, and the role of neurotransmitters such as dopamine, the specifics of it are not there yet so the following concepts are theoretical. So while associated research does point to particular areas of the brain involved with these processes we will skip the anatomy of the brain here.


We think of activities dogs do, such as sniffing, as natural behaviours. Researchers such as Jaak Panksepp in his emotional model of animals proposed that, actually, it is more than that and mammals such as dogs are intrinsically motivated to undertake activities such as foraging and to search and explore their environment for the good things that are out there.


So this is not considered to be a simple reward system or a means to determine which kinds of foods are tasty, it is an intrinsic impulse to search, explore and make sense of their environment.


Another researcher, Berridge (and associates) has proposed a model, considered to be more balanced by some, which breaks down the concept of reward into three components: 'LIKING', 'WANTING' and 'LEARNING'


WANTING is more or less equivalent to Panksepp's SEEKING and is characterised by what Berridge terms 'incentive salience' - an intrinsic motivation that facilitates approach to, and consumption of, something rewarding.

Items such as food (so natural rewards) will stimulate WANTING and the resulting behaviours of searching, sniffing etc. These behaviours are self-stimulating so the animals are motivated to keep doing it. The actual 'reward' of finding something pleasurable is almost an interruption as a different (consummatory) system kicks in to process the act of consuming the reward, once it has been obtained.


The LIKING response (following on with Berridge's approach) to the reward will, momentarily, inhibit 'WANTING' but, in our case, the dog will return to moving around foraging again.


Both Berridge and Panksepp agree that what really motivates animals to do things, including learning, is the anticipation of achieving a reward as opposed to consuming it. So WANTING/SEEKING are more important, or perhaps relevant, to the animal than LIKING - the response that occurs when the reward is obtained and consumed. Searching and investigating the environment is self-stimulating on an ongoing basis where a reward is a moment of pleasure.


An interesting sidebar on this relates to Simon Gadbois' 'Dopamine Hypothesis'. In his work on dogs undertaking scent work he found that traditional scent dogs such as hounds were not best suited to the work he needed them to do. While they had an incredible level of olfactory ability, it was not matched by the same level of motivation. The 'Dopamine Hypothesis' suggests that certain breeds have higher baseline levels of dopamine, the central neurotransmitter used in WANTING/SEEKING, and therefore important in olfaction and olfacto-motor behaviours (e.g. sniffing), which means that those breeds such as Border Collies tend to have a better all-round package of olfactory ability and work ethic to meet the demands of professional level scent work.


So if you have a Border Collie, Siberian Husky, Jack Russell or Parson's Terrier for example….you are on to a winner. For the rest of us, it's interesting, but means that our dogs will work for SPRINKLES (TM) because it is intrinsically and consequentially rewarding to do so although, as with most things dog, they will all do it differently!


But what Gadbois suggests from this is that the 'software', i.e. the dopamine levels and neural mechanisms are more important for these behaviours than the 'hardware'.


Gadbois & Reeve also put forward the idea that olfactory information is processed in a similar way to visual information (Schneider's WHAT? And WHERE?). For olfactory information the WHAT? system covers Detection, discrimination and identification of scents and a WHERE? System applies to being able to find the location of an item such as food.


So a dog can detect an item such as a SPRINKLE, discriminate it from any other scents around it that may be similar and, essentially know that is the item it is looking for. Although we know that canids are good at finding items like food but how they do it in the absence of other perceptual inputs (such as being able to see or hear the source) is still unknown and shows these processes to be yet more complex) so WHERE and beyond still has mysteries to be unlocked.


We have seen that dogs are designed to interact with their world primarily through their sense of smell. They have incredible abilities which we still do not fully understand the extent of. We have also considered that while the brain structures involved are generally known the specifics of how and where this neuro-cognitive processing of information occurs but what is known has led to the developing of concepts such as WANTING and SEEKING which show us that dogs are intrinsically inclined to sniff and search their environment for the good things contained within and that ability can be harnessed for pet dogs with activities such as SPRINKLES (TM)



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