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Nose (Olfactory System)

Dog's Olfactory System: Definition, Function, and Importance

A dog’s olfactory system is a network of interlinked structures responsible for its sense of smell. The olfactory system comprises the nose, nasal cavities, olfactory receptors, bulb, and olfactory nerve. The nasal structures work together to relay olfactory sensations to the brain. 

Dog noses function as their smelling system in daily life, gathering information about the environment and surroundings. Olfaction is an important sense in animals that developed through evolution. A lack of proper olfactory senses negatively impacts the dog’s daily activity. 

What is the Olfactory System in Dogs?

The olfactory system in dogs is a system of structures in the body that enable sense of smell. Canines are olfactory-driven rather than visually inclined like humans. Dogs extract information from their environment and detect signals through olfaction. 

The main function of the olfactory system is to translate odors into information the brain interprets. The sense of smell in dogs is a vital sense that they use for daily life. 

What is Olfaction in Dogs?

Olfaction in dogs is the sense of smell, which derives from detecting odorous substances. Dogs detect and identify odor more easily than humans. A dog’s sense of smell is acute and provides environmental information. 

The olfactory gland is a system of branched tubuloalveolar glands that produce mucus. Mucus is a lubricant of the olfactory epithelium that dissolves aerosolized odorants. 

The olfactory gland differs from sensory receptors because the olfactory gland is a specialized gland for the olfactory system. Sensory receptors are specialized cells that detect sensory stimuli and transform them into nerve impulses.

How does the Sense of Smell of Dogs Differ from Humans?

The sense of smell of dogs differs from humans because dogs have an additional organ called the vomeronasal organ or “Jacobsen’s Organ.” The vomeronasal is a part of the dog's olfactory system and is sensitive to chemicals such as pheromones in the air. Nerves in the vomeronasal organ are directly linked to the brain and respond to substances without distinct odor. 

The canine brain contains more olfactory receptors than human brains. The human nasal cavity has 6 million sensory receptor sites, whereas dogs have around 100 million. Research estimates that “dogs can smell anywhere from 1,000 to 10,000 times better than people”, according to Llera and Buzhardt of VCA Animal Hospitals. 

What are the Parts of the Olfactory System in Dogs?

The parts of the olfactory system in dogs are listed below.

  1. Olfactory Epithelium: The olfactory epithelium is membranous tissue in the nasal cavity. The epithelium comprises three cell types called the basal, olfactory, and sustentacular cells. A dog’s olfactory epithelium traps odors that pass across the cilia and relay the odors to the olfactory bulb for processing. “Dogs have significantly larger surface area of olfactory epithelium, with approximately 30% more ORs that can recognize a much larger variety of odorants” compared to humans, according to Jenkins et al., in a study entitled “When the Nose Doesn’t Know: Canine Olfactory Function Associated With Health, Management, and Potential Links to Microbiota,” 2018. 
  2. Nasal Cavity: The nasal cavity is the opening through which air enters the olfactory system. The cavity includes two chambers separated by a nasal septum. Each chamber has three turbinates (nasoturbinate, maxilloturbinate, and ethmoturbinate) that increase the mucosal surface area. The olfactory epithelium lines the interior nasal cavity. Increased contact time of air containing the odorant with the nasal cavity allows for odor detection. 
  3. Nasal Turbinates: The nasal turbinates are inside the nasal cavity and separated by the nasal septum, splitting into two chambers. Each chamber contains three turbinates called the nasoturbinata, maxilloturbinate, and ethmoturbinate. Turbinates resemble tunnels inside the nasal cavity that redirect airflow towards the pharynx. The turbinates increase mucosal surface area, which is necessary to allow contact time between the odorant and the olfactory cells of the olfactory epithelium. 
  4. Olfactory Bulb: The olfactory bulb is the processing center for olfaction. The bulb is a paired structure under the brain's frontal lobe that receives information from the cells in the nasal cavity. Each odorant is recognized by a unique combination of activated olfactory receptors, enabling the dog to identify different odors. 
  5. Olfactory Tract: The olfactory tract connects the olfactory bulb and the cerebral cortex. Tract connection bypasses the thalamus, making the olfactory pathway unique to other senses. The tract divides into the lateral, intermediate, and medial striae. Olfactory tracts are under the frontal lobe of the cerebrum. 
  6. Vomeronasal Organ (Jacobson's Organ): The vomeronasal organ is a paired tubular organ in the vomer bone in the proximal nasal septum sensitive to chemicals such as pheromones in the air. The nerves of the vomeronasal organ are linked to the brain and respond to substances lacking a distinct odor. 

What are the Common Problems in the Olfactory System of a Dog?

The common problems in the olfactory system of a dog are listed below. 

  1. Nasal Congestion: Nasal congestion is the obstruction of the nasal passages caused by inflammation, swelling, or excess mucus production, which impairs a dog's sense of smell and leads to breathing difficulties.
  2. Nasal Discharge: Nasal discharge is fluid or mucus from the nose that indicates underlying issues such as infections, allergies, or nasal trauma, impacting a dog's ability to breathe comfortably.
  3. Nasal Tumors: Nasal tumors are abnormal growths that develop within the nasal passages, obstructing airflow, causing nasal discharge, bleeding, and facial swelling, leading to changes in smell perception and respiratory problems.
  4. Nasal Polyps: Nasal polyps are non-cancerous growths that develop in dogs' nasal passages, causing nasal obstruction, difficulty breathing, and discomfort.
  5. Nasal Infections: Nasal infections occur when bacteria, viruses, or fungi invade the nasal passages, causing inflammation, nasal discharge, sneezing, and congestion.
  6. Nasal Trauma: Nasal trauma refers to injuries sustained to the nose, such as fractures, lacerations, or blunt force trauma, which result in pain, swelling, bleeding, and nasal deformities.
  7. Nasal Foreign Bodies: Nasal foreign bodies are objects lodged in the nasal passages, causing irritation, obstruction, and inflammation, leading to nasal discharge, sneezing, and discomfort, affecting a dog's ability to breathe correctly and detect odors.
  8. Nasal Deformities: Nasal deformities involve structural abnormalities or malformations of the nasal passages, which result from congenital defects, injuries, or underlying health conditions.
  9. Nasal Allergies: Nasal allergies in dogs occur when the immune system overreacts to allergens such as pollen, dust, or mold, resulting in inflammation, nasal congestion, sneezing, and nasal discharge.
  10. Age-related Changes: Age-related changes in the olfactory system include a decline in olfactory sensitivity and function and increased susceptibility to nasal issues such as congestion, infections, and nasal tumors, which affect a dog's overall sense of smell and respiratory health as they age.

1. Nasal Congestion

Nasal congestion is the narrowing of the nasal cavity. Rhinitis is a common cause of nasal problems in dogs due to upper respiratory malfunction. Rhinitis is the inflammation of the nasal mucous membranes and is accompanied by sinusitis, the inflammation of the nasal sinuses. 

Viral and bacterial infections, such as canine distemper, adenovirus types 1 and 2, kennel cough, and canine parainfluenza, cause nasal congestion in dogs. Allergic responses, such as allergic rhinitis, trigger nasal congestion and lacrimation. Inadequate airflow and filtration during nasal congestion expose the lungs to dust and microorganisms. 

Signs of nasal congestion in dogs are nasal discharge, crusting of the nasal planum, frequent pawing at the muzzle, sneezing, and an audible noise during breathing. 

Treatment for nasal congestion depends on the underlying cause. Consult a veterinarian to treat nasal congestion in dogs. 

2. Nasal Discharge

Nasal discharge is when fluid comes out of the nose. Rhinitis is a common cause of nasal discharge due to upper respiratory malfunction. The discharge varies from clear, mucoid, serosanguinous, and pustular. 

Viral and bacterial infections such as canine distemper, adenovirus types 1 and 2, kennel cough, and canine parainfluenza cause nasal discharge in dogs. Allergic responses, such as allergic rhinitis, trigger nasal discharge and lacrimation. Temperature fluctuations increase discharge coming from the nose to regulate the heat. 

Signs of rhinitis include nasal discharge, sneezing, snoring, open-mouth, and labored breathing. Treatment for nasal congestion depends on the underlying cause. Consult a veterinarian to treat nasal congestion in dogs.

3. Nasal Tumors

Nasal tumors are a type of cancer resulting from the uncontrolled production of cells that line the nasal airway. The most common form of nasal tumor in dogs is a nasal adenocarcinoma. The tumors are of epithelial cell origin in the nasal cavity. Exposure to cigarette smoke and living in urban environments are risk factors for nasal adenocarcinoma in dogs. 

Dogs with nasal tumors have discharge that is streaked with blood and exhibit noisy breathing, lethargy, and weight loss. Radiation therapy is the treatment of choice for dogs with adenocarcinoma. 

4. Nasal Polyps

Nasal polyps are noncancerous growths in the nose caused by chronic sinusitis. The polyps cause persistent irritation in the nasal cavity. Polyps do not spread to other body parts and are not considered dangerous. 

Signs of nasal polyps include sneezing, nasal discharge, nasal congestion, and polyp protrusion from the nostril. Treating nasal polyps relies on removing the trigger of sinusitis. Exposure to inhalant irritants such as dust, smoke, and cigarettes is a risk factor for the disease. Foreign bodies are a possible cause of frequent sinusitis. 

The recommended treatment for nasal polyps in dogs is surgical removal by a veterinarian.

5. Nasal Infections

Nasal infections are infectious diseases that lead to respiratory malfunction. Common respiratory diseases include canine distemper, adenovirus types 1 and 2, kennel cough, and canine parainfluenza. 

Nasal diseases are contagious and spread rapidly among dogs, especially unvaccinated dogs. Nasal infections compromise the upper and lower airways. Chronic nasal infections put the dog at risk for permanent damage. 

Nasal infections are treatable with antibiotics, antivirals, and proper management. Some respiratory nasal infections are self-limiting and only require symptomatic care. 

6. Nasal Trauma

Nasal trauma is when there is damage to the external or internal structures of the nose. Epistaxis or nose bleeding is a telltale sign of nasal trauma. Injuries to the snout and nose occur from self-inflicted injuries from pawing or accidental injuries from fighting or vehicular accidents. 

Large nasal tumors cause trauma due to the tumor’s extensive attachments to the underlying tissue and bones. Nasal trauma treatment depends on the severity and structures involved. Consult a veterinarian for specific nasal trauma treatment.

7. Nasal Foreign Bodies

Nasal foreign bodies are foreign structures that invade and clog the nasal cavity. Foreign bodies include grass, twigs, pieces of wood, bone pieces, or small stones. The lodged object causes discomfort and eventually leads to infection. 

Respiration is affected due to a narrowing of the upper airways. Signs of foreign bodies are frequent sneezing, pawing, and lacrimation. Treatment involves removing the lodged object. 

8. Nasal Deformities

Nasal deformities are changes in the normal anatomical structure of the nasal cavity. Some dogs, such as dogs with congenital palatal defects, have congenital abnormalities affecting the nasal structures. 

The defects include extensive craniomaxillofacial abnormalities that affect structures like the tympanic bullae, nasal turbinates, nasal septum, vomer, and sinuses. Nasal tumors cause facial deformities that affect the nose. Deformity increases based on the tumor size.

Dogs with nasal-facial defects from subsequent injury have nasal deformities. The treatment for deformities involves successive reconstructive surgery by a veterinarian.

9. Nasal Allergies

Nasal allergies are allergen-induced inflammation of the nasal cavity. The most common cause of nasal allergies in dogs is allergic rhinitis or sinusitis, which occurs seasonally associated with pollen production. 

Inhalant allergies include cigarette smoke, irritant gases, dust, or mold. Signs of allergic rhinitis in dogs are sneezing, pawing, lacrimation, nasal discharge, and loud breathing. The signs are accompanied by inflammatory signs all over the body. 

The treatment of dog allergies is medication such as antihistamines or steroids and avoidance of the irritant. 

10. Age-related Changes

Age-related changes occur when the sense of sense deteriorates from old age. The term for this phenomenon is called “sensory loss” in aged pets. “Histopathologic changes to the olfactory epithelium occur with aging, and surveys have suggested an owner perception of olfaction and other sensory decline in aging pet dogs,” according to Khan et al., in the study entitled “A novel task of canine olfaction for use in adult and senior pet dogs,” 2023. 

Treatment of age-related changes involves regular veterinary check-ups to monitor the dog’s health.

What is the Consequence of Leaving the Nose Problem Untreated?

The consequence of leaving the nose problem untreated is permanent damage to the olfactory structures. Persistent infection and trauma are common causes of respiratory malfunction in dogs. 

Invasive tumors affect the underlying bone, tissue, and vessels that supply essential olfactory structures. Respiratory problems are uncomfortable for dogs and reduce their willingness to engage in daily activities. Anti-inflammatory supplements such as CBD are easily available for dogs with nasal problems. 

CBD oil shows promising results on cell cultures from different canine cancers. CBD oil for canine cancercaused a significant decrease in cancer cell reproduction in all cell lines studied. Use of CBD-rich whole help extract was able to reduce cancer cell reproduction at lower concentrations than CBD oil alone”, according to Wakshlag, in a study entitled “Effects of Cannabidiol on Canine Neoplastic Cell Apoptosis/Autophagy and Potential for Chemotherapy Resistance or Sensitivity,” 2021. 

How is the Ability of Dogs to Detect Scent?

The ability of dogs to detect scent is an interlinked system of transmission of an odorant substance. Dogs have over 100 million sensory receptor sites in the nasal cavity that aid in detecting, identifying, and locating scents. 

Dogs have an additional olfactory organ called the Jacobsen’s organ that is acute to pheromones in the air. The organ is directly linked to the brain and identifies substances lacking a distinct odor. 

Pheromones are invisible chemicals aerosolized in the air and alter physiological and psychological changes in dogs. For example, a dog determines if a member of the opposite sex is available for breeding. Scent detection is an essential ability in canine olfaction. 

What Factors Influence the Functionality of a Dog's Olfactory System?

The factors that influence the functionality of a dog’s olfactory system are listed below. 

  • Breed: German Shepherds, Belgian Malinois, Bloodhounds, Beagles, Dachshunds, Golden Retrievers, and Labrador Retrievers have an excellent sense of smell. The breeds are used in bomb and drug detection, search and rescue, and as guide dogs. 
  • Genetics: Some dogs are born with anatomical abnormalities that affect their sense of smell. Dogs with facial bone, palate, and nasal deformities are likely to have less acute smell. Nasal tumors are observable in medium-large breeds with long noses. 
  • Age: Sensory loss occurs with aging. Olfactory sensors wane, making olfaction harder for old and senior dogs. 
  • Health: Underlying health conditions affect dogs' sense of smell. Respiratory infections, viruses, and cancers affect vital structures in the olfactory system, and recurrent respiratory diseases cause permanent damage.
  • Training and Experience: Specialized training enhances olfactory skills in working dogs. Increased training and experience lets the dog detect odorants more quickly or from further away. 
  • Environment: Dogs living in a polluted environment are prone to allergic rhinitis. Inhalant irritants such as car smoke, cigarette smoke, dust, and molds are able to trigger nasal congestion or allergies that affect the sense of smell. 
  • Motivation: Training helps the dog establish an interest in smelling their surroundings. Food training is a positive reinforcement when the dog identifies an appealing smell.  
  • Nutrition: Dietary fat has been shown to influence canine olfaction. A study performed on seventeen certified detection dogs showed that “dogs on the high PUFA (Polyunsaturated fatty acids) diet utilising maize oil showed mild improvement in olfaction”, according to Angle et. al. in a study entitled “The effects of exercise and diet on olfactory capability in detection dogs,” 2014.
  • Hormonal Status: Pheromones are aerosolized, and canine olfaction detects chemical signals. Dogs in heat during breeding season release higher amounts of pheromones as a chemical marker of receptivity. 
  • Stress and Emotional State: Stress impacts a dog's olfactory senses by limiting their ability to detect and interpret scents. Stressed or anxious dogs experience hormone level and respiratory rate changes, affecting their sense of smell and decreasing focus.

What type of Dog Breed has the Most Sensitive Sense of Smell?

Working dogs have the most sensitive sense of smell. Breeds such as German Shepherds, Belgian Malinois, Bloodhounds, Beagles, Dachshunds, Golden Retrievers, and Labrador Retrievers have excellent senses of smell. The breeds excel in military work, such as bomb and drug detection and search and rescue. Some dogs are used as guide dogs for the blind or in detecting low blood sugar and seizures. 

What is the Importance of the Olfactory System in Dogs?

The importance of the olfactory system in dogs is crucial to understanding how they perceive reality. A dog’s nose is highly sensitive and has more olfactory sensors than humans. Canine olfactory senses evolved due to centuries of hunting and survival prior to domestication. 

Olfaction is how dogs gather information about their surroundings. The dog is able to sense danger, find out its location, locate food, make its way home, and identify its pack members. The nose anatomy in dogs is the most widely used system of organs. Dogs with a poor sense of smell are prone to accidents and lack a sense of awareness that influences their survival rate.