Dog sense of smell

Last updated
Scent hounds, especially the bloodhound, are bred for their keen sense of smell. Bloodhund r54.jpg
Scent hounds, especially the bloodhound, are bred for their keen sense of smell.

The dog sense of smell is the most powerful sense of this species, the olfactory system of canines being much more complex and developed than that of humans. [1] It is believed to be up to 10 million times as sensitive as a human's in specialized breeds. Dogs have roughly forty times more smell-sensitive receptors than humans, ranging from about 125 million to nearly 300 million in some dog breeds, such as bloodhounds. [1] These receptors are spread over an area about the size of a pocket handkerchief (compared to 5 million over an area the size of a postage stamp for humans). [2] [3] Dogs' sense of smell also includes the use of the vomeronasal organ, which is used primarily for social interactions.

Contents

The dog has mobile nostrils that help it determine the direction of the scent. Unlike humans, dogs do not need to fill up their lungs as they continuously bring odors into their noses in bursts of 3-7 sniffs. Dog noses have a bony structure inside that humans do not have, which allows the air that has been sniffed to pass over a bony shelf to which odor molecules adhere. The air above this shelf is not washed out when the dog breathes normally, so the scent molecules accumulate in the nasal chambers and the scent builds with intensity, allowing the dog to detect the faintest of odors and can even detect emotions. [4] : 247 

One study into the learning ability of dogs compared to wolves indicated that dogs have a better sense of smell than wolves when locating hidden food, but there has yet been no experimental data to support this view. [5]

A typical dog's nose Dogs Nose.png
A typical dog's nose

The wet nose, or rhinarium, is essential for determining the direction of the air current containing the smell. Cold receptors in the skin are sensitive to the cooling of the skin by evaporation of the moisture by air currents. [6]

Function and mechanism

A great part of a dog's brain is dedicated to acquiring and interpreting odors, using its nose as a guide in sniffing in order to follow a trail. The animal performs a series of short inhalations and expirations, permitting it to bring the odor-bearing molecules in contact with its olfactory mucosa. These molecules are dissolved and then absorbed by cells of the olfactory epithelium before they reach neurons, which transmit information to the brain. Dogs with elongated noses perform better than dogs with a flat noses. Additionally, larger dogs have a better sense of smell than smaller dogs. [7]

A dog's nose is significantly colder than their body temperature. This makes it more sensitive to thermal radiation. Dogs can thus detect even weak levels of warmth. [8]

Dogs are able to smell from birth and develops during the first two weeks of their life. Dogs can also learn scents in the womb. Soon after birth, dogs use their sense of smell to recognize their mothers. A dog is also able to identify foods which his mother has ingested, having learned their smells before birth. [9]

When dogs sniff, they start by using only their right nostril. If they are comfortable with the smell, they then begin using their left nostril. This supports the theory that dogs process novel information using the right hemisphere of their brain, and the left for reacting to familiar situations. As dogs sniff, air travels along an upper and lower pathway. The lower pathway, where the majority of the air travels, leads to the lungs, while the upper pathway leads to olfactory receptors which detect scents. The lower pathway is also used for exhalation, allowing odor molecules to accumulate on the receptors. [10]

Use in communication

Scent is used extensively in canine communication. Dogs may sniff each other directly, or may communicate through chemical signals. In direct contact, male dogs focus more on the rear ends of the dog which they are sniffing, while females tend to sniff the head. When communicating through chemical signals, the most common form of communication is urine-marking. Dogs can detect different qualities in another dog's urine, which may communicate information such as social status or sex. [10]

Comparison to humans

Dogs have vastly more powerful noses than humans. The typical dog's nose is 100,000 to 1 million times as sensitive as a human's, and the most sensitive breed, the bloodhound, has a sense of smell which can be up to 100 million times as sensitive. Additionally, dogs have much larger olfactory mucosa and a larger part of the brain dedicated to odors. Whereas in humans, 5% of the brain is dedicated to odors, in dogs this figure is 33%. Dogs are able to detect odors 9 orders of magnitude more faint than humans, who can detect odors up to 1 ppb. [9] : 30 

Conditions affecting ability

Many factors can affect a dog's ability to smell, including age, sex, breed, disease, diet and environmental conditions. As dogs grow older, their performance and ability to learn new smells is reduced. Female dogs have a greater sense of smell than males. A variety of diseases can decrease a dog's sense of smell, such as canine distemper and nasal mites. Dogs have an enhanced sense of smell when fed a high-fat, low-protein diet. There are a number of theories for this. [9] : 31–32 

Humidity improves a dog's ability to detect scents, due to lingering odors trapped by water vapor and increased humidity within the dog's nose. Higher temperatures increase the presence of odor molecules in the air, especially at the level of a dog's nose, but kill bacteria useful in detecting scents and can decrease a dog's ability to work. [9] : 87  [10]

Wind also has an effect on a dog's sense of smell. Winds which are too low decrease effective range, while winds which are too high make detection difficult. The optimal range is 3 to 10 km/h. [9] : 88  Turbulence reduces a dog's ability to track scents. [9] : 91 

Use of ability by humans

Humans learned to use dogs' exceptional sense of smell, primarily for hunting but also, more recently, for diverse types of searches. [10] [9]

Law enforcement

Dogs have been used for a variety of law enforcement activities.

Rescue

Dogs have been used for search and rescue operations.

Detection of disease

Some studies have found that certain dogs are able to detect diseases among human beings, notably cancer. The British medical journal The Lancet , suggested for the first time in 1989 the use of dogs to detect cancer. [11]

Hunting dogs

Employed for various purposes in hound-hunting, the hunting dog is above all used for its tracking abilities, that is finding and sniffing out prey.

Truffle dogs

This type of dog has been trained and raised to find truffles buried in the ground.

Competitions [12]

There are scent work trials available in multiple different countries, which test the dogs ability to find and indicate odours to the handler. The scents used in these classes, called target odors are:

The American Kennel Club has 4 different search environments: Container, Interior, Exterior, Buried. There is also an advanced level, called detective for high-achieving dogs. In this level, the search includes a mix of all the search environments.

See also

Related Research Articles

<span class="mw-page-title-main">Olfactory nerve</span> Cranial nerve I, for smelling

The olfactory nerve, also known as the first cranial nerve, cranial nerve I, or simply CN I, is a cranial nerve that contains sensory nerve fibers relating to the sense of smell.

Stimulus modality, also called sensory modality, is one aspect of a stimulus or what is perceived after a stimulus. For example, the temperature modality is registered after heat or cold stimulate a receptor. Some sensory modalities include: light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation. All sensory modalities work together to heighten stimuli sensation when necessary.

<span class="mw-page-title-main">Olfactory system</span> Sensory system used for smelling

The olfactory system, or sense of smell, is the sensory system used for olfaction. Olfaction is one of the special senses directly associated with specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli.

<span class="mw-page-title-main">Olfactory receptor</span> Chemoreceptors expressed in cell membranes of olfactory receptor neurons

Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants which give rise to the sense of smell. Activated olfactory receptors trigger nerve impulses which transmit information about odor to the brain. In vertebrates, these receptors are members of the class A rhodopsin-like family of G protein-coupled receptors (GPCRs). The olfactory receptors form the largest multigene family in vertebrates consisting of around 400 genes in humans and 1400 genes in mice. In insects, olfactory receptors are members of an unrelated group of ligand-gated ion channels.

<span class="mw-page-title-main">Androstenone</span> Chemical compound

Androstenone (5α-androst-16-en-3-one) is a 16-androstene class steroidal pheromone. It is found in boar's saliva, celery cytoplasm, and truffle fungus. Androstenone was the first mammalian pheromone to be identified. It is found in high concentrations in the saliva of male pigs, and, when inhaled by a female pig that is in heat, results in the female assuming the mating stance. Androstenone is the active ingredient in 'Boarmate', a commercial product made by DuPont sold to pig farmers to test sows for timing of artificial insemination.

The vibration theory of smell proposes that a molecule's smell character is due to its vibrational frequency in the infrared range. This controversial theory is an alternative to the more widely accepted docking theory of olfaction, which proposes that a molecule's smell character is due to a range of weak non-covalent interactions between its protein odorant receptor, such as electrostatic and Van der Waals interactions as well as H-bonding, dipole attraction, pi-stacking, metal ion, Cation–pi interaction, and hydrophobic effects, in addition to the molecule's conformation.

<span class="mw-page-title-main">Tracking (dog)</span> Ability of dogs to recognize and follow a specific scent

Tracking refers to a dog's ability to detect, recognize and follow a specific scent. Possessing heightened olfactory abilities, dogs, especially scent hounds, are able to detect, track and locate the source of certain odours. A deeper understanding of the physiological mechanisms and the phases involved in canine scent tracking has allowed humans to utilize this animal behaviour in a variety of professions. Through domestication and the human application of dog behaviour, different methods and influential factors on tracking ability have been discovered. While tracking was once considered a predatory technique of dogs in the wild, it has now become widely used by humans.

In medicine and anatomy, the special senses are the senses that have specialized organs devoted to them:

<span class="mw-page-title-main">Rhinarium</span> Surface around the nostrils in some mammals

The rhinarium is the furless skin surface surrounding the external openings of the nostrils in many mammals. Commonly it is referred to as the tip of the snout, and breeders of cats and dogs sometimes use the term nose leather. Informally, it may be called a "truffle", "wet snout," or "wet nose” because its surface is moist in some species: for example, healthy dogs and cats.

Canine cancer detection is an approach to cancer screening that relies upon the claimed olfactory ability of dogs to detect, in urine or in breath, very low concentrations of the alkanes and aromatic compounds generated by malignant tumors. While some research has been promising, no verified studies by secondary research groups have substantiated the validity of positive, conclusive results.

<span class="mw-page-title-main">Electronic nose</span> Electronic sensor for odor detection

An electronic nose is an electronic sensing device intended to detect odors or flavors. The expression "electronic sensing" refers to the capability of reproducing human senses using sensor arrays and pattern recognition systems.

<span class="mw-page-title-main">Odor</span> Volatile chemical compounds perceived by the sense of smell

An odor or odour is a smell or a scent caused by one or more volatilized chemical compounds generally found in low concentrations that humans and many animals can perceive via their olfactory system. While smell can refer to pleasant and unpleasant odors, the terms scent, aroma, and fragrance are usually reserved for pleasant-smelling odors and are frequently used in the food and cosmetic industry to describe floral scents or to refer to perfumes.

<span class="mw-page-title-main">Sense of smell</span> Sense that detects smells

The sense of smell, or olfaction, is the special sense through which smells are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste.

Olfactory memory refers to the recollection of odors. Studies have found various characteristics of common memories of odor memory including persistence and high resistance to interference. Explicit memory is typically the form focused on in the studies of olfactory memory, though implicit forms of memory certainly supply distinct contributions to the understanding of odors and memories of them. Research has demonstrated that the changes to the olfactory bulb and main olfactory system following birth are extremely important and influential for maternal behavior. Mammalian olfactory cues play an important role in the coordination of the mother infant bond, and the following normal development of the offspring. Maternal breast odors are individually distinctive, and provide a basis for recognition of the mother by her offspring.

A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as such, many more are now recognized. Senses used by non-human organisms are even greater in variety and number. During sensation, sense organs collect various stimuli for transduction, meaning transformation into a form that can be understood by the brain. Sensation and perception are fundamental to nearly every aspect of an organism's cognition, behavior and thought.

<span class="mw-page-title-main">Sniffing (behavior)</span> Nasal inhalation to sample odors

Sniffing is a perceptually-relevant behavior, defined as the active sampling of odors through the nasal cavity for the purpose of information acquisition. This behavior, displayed by all terrestrial vertebrates, is typically identified based upon changes in respiratory frequency and/or amplitude, and is often studied in the context of odor guided behaviors and olfactory perceptual tasks. Sniffing is quantified by measuring intra-nasal pressure or flow or air or, while less accurate, through a strain gauge on the chest to measure total respiratory volume. Strategies for sniffing behavior vary depending upon the animal, with small animals displaying sniffing frequencies ranging from 4 to 12 Hz but larger animals (humans) sniffing at much lower frequencies, usually less than 2 Hz. Subserving sniffing behaviors, evidence for an "olfactomotor" circuit in the brain exists, wherein perception or expectation of an odor can trigger brain respiratory center to allow for the modulation of sniffing frequency and amplitude and thus acquisition of odor information. Sniffing is analogous to other stimulus sampling behaviors, including visual saccades, active touch, and whisker movements in small animals. Atypical sniffing has been reported in cases of neurological disorders, especially those disorders characterized by impaired motor function and olfactory perception.

Odor molecules are detected by the olfactory receptors in the olfactory epithelium of the nasal cavity. Each receptor type is expressed within a subset of neurons, from which they directly connect to the olfactory bulb in the brain. Olfaction is essential for survival in most vertebrates; however, the degree to which an animal depends on smell is highly varied. Great variation exists in the number of OR genes among vertebrate species, as shown through bioinformatic analyses. This diversity exists by virtue of the wide-ranging environments that they inhabit. For instance, dolphins that are secondarily adapted to an aquatic niche possess a considerably smaller subset of genes than most mammals. OR gene repertoires have also evolved in relation to other senses, as higher primates with well-developed vision systems tend to have a smaller number of OR genes. As such, investigating the evolutionary changes of OR genes can provide useful information on how genomes respond to environmental changes. Differences in smell sensitivity are also dependent on the anatomy of the olfactory apparatus, such as the size of the olfactory bulb and epithelium.

Retronasal smell, retronasal olfaction, is the ability to perceive flavor dimensions of foods and drinks. Retronasal smell is a sensory modality that produces flavor. It is best described as a combination of traditional smell and taste modalities. Retronasal smell creates flavor from smell molecules in foods or drinks shunting up through the nasal passages as one is chewing. When people use the term "smell", they are usually referring to "orthonasal smell", or the perception of smell molecules that enter directly through the nose and up the nasal passages. Retronasal smell is critical for experiencing the flavor of foods and drinks. Flavor should be contrasted with taste, which refers to five specific dimensions: (1) sweet, (2) salty, (3) bitter, (4) sour, and (5) umami. Perceiving anything beyond these five dimensions, such as distinguishing the flavor of an apple from a pear for example, requires the sense of retronasal smell.

Smell as evidence of disease has been long used, dating back to Hippocrates around 400 years BCE. It is still employed with a focus on volatile organic compounds (VOCs) found in body odor. VOCs are carbon-based molecular groups having a low molecular weight, secreted during cells' metabolic processes. Their profiles may be altered by diseases such as cancer, metabolic disorders, genetic disorders, infections, and among others. Abnormal changes in VOC composition can be identified through equipment such as gas chromatography-mass spectrometry(GC-MS), electronic nose (e-noses), and trained non-human olfaction.

<span class="mw-page-title-main">Olfactic communication</span> Social interaction through smell

Olfactic communication is a channel of nonverbal communication referring to the various ways people and animals communicate and engage in social interaction through their sense of smell. Our human olfactory sense is one of the most phylogenetically primitive and emotionally intimate of the five senses; the sensation of smell is thought to be the most matured and developed human sense.

References

  1. 1 2 Coren, Stanley (2004). How Dogs Think. First Free Press, Simon & Schuster. ISBN   0-7432-2232-6.[ page needed ]
  2. ↑ "Understanding a Dog's Sense of Smell". Dummies.com. Archived from the original on 9 March 2008. Retrieved 2008-10-22.
  3. ↑ "The Dog's Sense of" (PDF). Alabama and Auburn Universities. Archived from the original (PDF) on 11 January 2012. Retrieved 2008-10-22.
  4. ↑ Coren, Stanley (2000). How To Speak Dog: Mastering the Art of Dog-Human Communication. New York: Simon & Schuster
  5. ↑ Virányi, Z. F.; Range, F. (2013). "Social learning from humans or conspecifics: Differences and similarities between wolves and dogs". Frontiers in Psychology. 4: 868. doi: 10.3389/fpsyg.2013.00868 . PMC   3849518 . PMID   24363648.
  6. ↑ Dijkgraaf S.; Vergelijkende dierfysiologie; Bohn, Scheltema en Holkema, 1978, ISBN   90-313-0322-4
  7. ↑ "L'odorat chez les chiens : Secrets et capacités suprenantes". Hector Kitchen (in French).
  8. ↑ Bálint, Anna; Andics, Attila; Gácsi, Márta; Gábor, Anna; Czeibert, Kálmán; Luce, Chelsey M.; Miklósi, Ádám; Kröger, Ronald H. H. (2020). "Dogs can sense weak thermal radiation". Scientific Reports. 10 (1): 3736. Bibcode:2020NatSR..10.3736B. doi:10.1038/s41598-020-60439-y. PMC   7048925 . PMID   32111902.
  9. 1 2 3 4 5 6 7 Rosell, Frank; Bekoff, Marc; Oatley, Diane (2018). Secrets of the Snout. doi:10.7208/chicago/9780226536538.001.0001. ISBN   978-0-226-53636-1.: 27 
  10. 1 2 3 4 Kokocińska-Kusiak, Agata; Woszczyło, Martyna; Zybala, Mikołaj; MacIocha, Julia; Barłowska, Katarzyna; Dzięcioł, Michał (2021). "Canine Olfaction: Physiology, Behavior, and Possibilities for Practical Applications". Animals. 11 (8): 2463. doi: 10.3390/ani11082463 . PMC   8388720 . PMID   34438920.
  11. ↑ Williams, Hywel; Pembroke, Andres (1989). "Sniffer Dogs in the Melanoma Clinic?". The Lancet. 333 (8640): 734. doi:10.1016/s0140-6736(89)92257-5. PMID   2564551.
  12. ↑ "AKC Scent Work". American Kennel Club. Retrieved 2024-10-05.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.