Mullins Dog Training- Blood Tracking Dogs

By Kenny Mullins, Mullins Dog Training

The Canine Scent Superpower

Dogs experience the world primarily through their noses. They have up to 300 million olfactory receptors in their nasal cavities, compared to about six million in humans . Additionally, the portion of a dog’s brain dedicated to analyzing smells is 40 times larger than ours in relative size . These biological advantages mean a dog’s sense of smell is estimated to be 10,000 to 100,000 times more acute than a human’s . For example, while we might notice if a cup of coffee has a teaspoon of sugar added, a dog could detect the same teaspoon in a million gallons of water .

However, it’s not just the sheer number of receptors that makes dogs superior scent trackers, it’s how they interpret and process scent information. A well-trained dog can discern incredibly subtle differences in scent concentration. In one study, dogs brought to a footprint trail could determine the direction a person walked after only a few steps, because the first footprints had slightly less scent (having had more time to dissipate) than later ones . This astounding ability to detect minute odor differences showcases the dog’s scent-processing prowess. In other words, the dog’s “nose” isn’t just in its nostrils,  it’s also in its brain, making sense of a complex scent picture. This is why training and experience are so important: a dog that learns how to interpret scent cues will outperform others, even if they all possess powerful noses. The emphasis should be on honing the dog’s natural scent discrimination ability, rather than worrying solely about the count of olfactory receptors.

The Hidden Power of Turbinates and Nose Length

A major factor in a dog’s superior scenting ability lies deep inside its nose,  in structures called turbinates. Turbinates are intricate, scroll-like bones covered in scent receptor cells, dramatically increasing the surface area inside the nasal cavity. In fact, if you could unroll and flatten a dog’s turbinates, the scent-detecting surface could stretch over the size of a full sheet of paper,  far larger than a human’s scent area. These complex structures allow air to be efficiently filtered and passed over millions of olfactory receptors. The relationship between a dog’s nose length and its scenting ability is directly tied to turbinate structure: longer-nosed breeds have more room for expanded turbinates, allowing them to process more scent molecules at once. While even short-nosed breeds like Beagles are excellent scenters, dogs bred for tracking wounded game often have longer snouts to maximize the surface area available for scent detection. However, as with all tracking work, scent interpretation, not just physical nose structure, ultimately determines success.

Jacobson’s Organ: A Second Nose for Pheromones

Beyond their main scent receptors, dogs have an additional olfactory tool that humans lack: the vomeronasal organ, also known as Jacobson’s organ. This special organ, located in the roof of a dog’s mouth (just behind the upper incisors), is designed to detect pheromones, chemical signals released by animals . When a dog wrinkles its nose and even pulls back its lips (sometimes called the Flehmen response), it is drawing scent molecules toward this organ to analyze pheromonal cues. Jacobson’s organ has its own direct nerve pathways to the brain, separate from the regular olfactory system, which means pheromonal information is processed in a dedicated part of the dog’s brain . It’s essentially a second “nose” focused on biologically significant scents like pheromones.

Dogs use Jacobson’s organ to gather information that goes beyond just identifying a smell, it helps them detect the emotional and physiological state of other creatures. Research confirms that dogs can smell pheromones or hormone-based scents and discern how another animal is feeling or even detect if it’s unhealthy . For instance, dogs sniffing each other’s bodies (especially around the rear, where pheromone-secreting glands are located) can figure out a companion’s mood and health status from those chemical signals . Unlike humans, who largely rely on visual cues and language, dogs rely on this rich chemical communication. The Jacobson’s organ essentially allows a dog to “read the invisible news” left behind by other animals,  from mating readiness in the case of social pheromones to the emotional state of an animal in distress. This capability is key when training tracking dogs to follow wounded game.

What Are “Declining Health Pheromones”?

Declining health pheromones refer to the scent signals emitted by an animal that is injured, highly stressed, or whose health is deteriorating. In the past, trainers often casually called these “fear pheromones,” but the term declining health pheromones is more precise and professionally descriptive of the phenomenon. When a deer or other game animal is wounded and in distress, its body undergoes physiological changes: stress hormones like adrenaline and cortisol spike, and the animal’s glands and organs may release distinct chemicals as its condition worsens. These chemicals create a scent profile that a well-trained dog can detect and differentiate from all other background odors. In essence, it’s the smell of an animal in crisis, a combination of stress-induced odors and metabolic byproducts that signal the creature’s declining vitality.

Dogs trailing a wounded animal aren’t just following the smell of blood,  often there isn’t much blood at all on a difficult track, but rather they are keying in on this invisible pheromonal scent trail. To a tracking dog, a mortally wounded deer “smells” different from a healthy one sprinting away. The stressed animal is emitting a continuous stream of scent indicators that something is wrong. Scientific studies on canine abilities back this up: for example, dogs can even smell when a human is stressed versus calm, just from sweat and breath samples . If dogs can detect human stress with such accuracy, it stands to reason that they can also sense when a prey animal is panicked or weakening. The concept of declining health pheromones encapsulates this idea,  that as long as the wounded animal is alive and its health is deteriorating, it is actively releasing scent cues that signal its condition to tracking dogs.

It’s important to note that these pheromonal cues are species-specific in origin (a deer’s unique chemical cocktail of stress), but a dog’s nose and brain are perfectly capable of picking them up across many species. The tracking dog effectively recognizes the smell of distress. At Mullins Dog Training, we train our dogs to home in on these particular scent cues, conditioning them to treat the “declining health” scent as a beacon leading to the injured game. By focusing on these pheromones, even an inexperienced handler can understand why a dog might suddenly veer off the visible blood trail,  the dog is sensing the wind-carried trail of the animal’s fear and failing health, which might drift differently than the ground scent.

Scent Trail Duration and Dissipation

A critical question for trackers is: How long do these scent trails last? Understanding scent dissipation is vital for making decisions on when to deploy a dog after an animal is shot or injured. Updated information and experience indicate that declining health pheromones persist for as long as the animal is alive and in distress, but begin to fade once the animal’s condition stabilizes or it dies. In practical terms, as long as a deer is moving, frightened, and losing blood or condition, it continues to leave an odor plume of stress and health-decline pheromones along its path. This pheromone scent can be quite persistent in the immediate hours following the shot. Under optimal conditions, cool temperatures, moist air (which helps preserve scent), and minimal wind,  a well-trained dog can follow a trail that is 24 hours old and even older. In fact, there are many documented cases of dogs successfully tracking and finding game more than 48+ hours after injury, especially if the trail wasn’t contaminated, and conditions were ideal. Experienced dogs have been known to follow human scent trails that are several days old , and while a deer’s trail is different, this illustrates how long scent molecules can remain detectable in general.

That said, time is still of the essence when it comes to tracking. The strongest, freshest trail will always be easier for the dog to follow. As time passes, several things happen: the volatile components of the scent (both odor and pheromones) start to evaporate or disperse, weather conditions can dilute scent, and the wounded animal (if still mobile) may travel farther from the point of impact. If the animal expires (dies) or begins regaining itself, it will no longer produce the declining health pheromones that the dog has been tracking. At that point, the only remaining scent might be residual pheromones clinging to vegetation, the smell of blood (which may be scant), and eventually the onset of decomposition odors if enough time passes after the expiration of the animal. 

Updated scent-dissipation insight: once the source of the pheromone (the animal) is gone, a pheromone-based trail will begin to diminish. For example, if a deer succumbs overnight, by morning the pheromonal component of the trail may be faint, depending on conditions. The dog might then have to rely more on lingering scent, such as bacteria growth, or the general smell of the carcass itself if it gets close. This is why professional trackers often prefer to put a dog on the trail sooner rather than later, but not too soon, ideally within the first day post-injury, to capitalize on the strongest scent signal before it fades.

It’s also worth noting that different scent components dissipate at different rates. Blood droplets on the ground can dry and lose scent strength (though dried blood can still be smelled by a dog for quite some time due to bacteria growth). In contrast, pheromonal scents that waft off on the breeze might travel farther initially but also disperse more quickly into the air. A cool, damp morning might preserve ground scent well, whereas a hot noon sun can bake and lift odors away. Every tracking scenario will be a bit different. As part of our training at Mullins Dog Training, we educate handlers on reading their dog’s behavior in relation to scent conditions; for instance, if a dog is casting widely with nose in the air, it might be hunting for wisps of the airborne pheromone scent, whereas nose-down, deliberate sniffing might indicate it’s following ground scent like blood or footprints.

From Nose to Brain: Interpretation is Key

All of this science and scent ability culminates in one key lesson: a dog’s effectiveness in tracking ultimately comes down to scent interpretation. Every dog has an incredible nose by human standards, but the truly great trackers are those who learn (through training and experience) to focus on the right scent and to filter out distractions. Think of it this way, a dog’s nose gathers the data, but it’s the dog’s brain that interprets it and decides “this is the wounded deer I need to follow.” Dogs naturally love to follow interesting smells, but training refines their instinct to zero in on a specific target odor (like a particular deer’s trail) and stick with it with determination.

Moreover, dogs can make decisions based on the scent information they pick up. They aren’t passive scent receivers; they are active scent interpreters. For example, a skilled tracking dog may reach a spot where the wounded deer doubled back or veered sharply, and there may be confusing cross-trails. A lesser-trained dog might get bewildered, but an experienced dog will piece together the puzzle, noticing perhaps that one direction has the stronger smell of the “declining health pheromone” and following that, effectively reasoning out the correct path. This problem-solving aspect of scent work is what separates an ordinary dog from a superb tracking dog.

It’s also fascinating to observe that dogs can become pessimistic or concerned when they sniff certain scents, a reflection of their interpretation of what the scent means. A recent study even showed that the smell of human stress can affect a dog’s emotional state, which we often see when judging in testing scenarios. In a tracking scenario, when a dog hits upon the strong scent of a badly wounded animal, you might see the dog visibly intensity in focus, as if it understands the gravity of the find at the end of the trail. Handlers learn to recognize these subtleties: a change in tail wag, a new urgency in the dog’s movement, or the dog lifting its head to catch wind-borne odor could all signal that the dog has picked up on an important pheromonal cue from the quarry.

Conclusion: Training the Ultimate Tracking Dog

Mullins Dog Training believes in leveraging all aspects of a dog’s natural abilities, from the millions of olfactory receptors, to the amazing Jacobson’s organ, to the canine brain’s analytical might, to train the ultimate tracking partners for wounded game recovery. By understanding concepts like declining health pheromones, handlers can better appreciate what their dogs are sensing and why they behave the way they do on a trail. Remember, a dog is not just following a splash of blood; it’s reading a whole story written in scent. The key to success is trusting the dog’s nose and intuition, and guiding it with proper training and handling techniques.

In summary, when it comes to scent tracking, quality beats quantity. A dog may have an astounding nose (with physical advantages over humans), but it’s the cultivation of the dog’s interpretative skill and focus that truly unlocks spectacular tracking performances. Dogs use their noses and Jacobson’s organs to detect what we cannot – the panic of a fleeing animal, the chemical cries of distress, the faint footprint hours old, and then use their brains to assemble those clues into a path to follow. With updated knowledge about scent longevity and a deeper respect for the dog’s sensory world, we can improve our training methods and recovery rates for wounded game.

Mullins Dog Training – Specializing in Blood Tracking Dogs for Wounded Game – remains committed to using science-based, compassionate training to produce dogs that excel in the field. By staying informed about research and continuously refining techniques, we ensure that both our dogs and clients are equipped with cutting-edge understanding. A handler who knows about declining health pheromones and canine scent interpretation will work with their dog more effectively, resulting in faster finds and ethical recoveries. Trust your dog, train diligently, and let their nose, and that incredible second nose, Jacobson’s organ, lead the way to success.