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Equine Respiratory System & Equine Smell (Olfactory Ability) Overview

The horse's respiratory system consists of the nostrils, pharynx, larynx, trachea, diaphragm, and lungs. Additionally, the nasolacrimal duct and sinuses are connected to the nasal passage. The horse's respiratory system not only allows the animal to breathe, but also is important in the horse's sense of smell (olfactory ability) as well as in communication.

Equine Respiratory System: The horse's respiratory system consists of the nostrils, pharynx, larynx, trachea, diaphragm, and lungs. Additionally, the nasolacrimal duct and sinuses are connected to the nasal passage. The horse's respiratory system not only allows the animal to breathe, but also is important in the horse's sense of smell (olfactory ability) as well as in communicating.

The respiratory system moves air containing oxygen from outside the body to inside the lungs bringing the oxygen as close as possible to the blood in the circulation.
Air moving outside the body passes first through the upper respiratory system including the nostrils, the nasal passages and larynx and then into the trachea (or windpipe).
The respiratory system moves air containing oxygen from outside the body to inside the lungs bringing the oxygen as close as possible to the blood in the circulation.
Locomotor Respiratory Coupling (LRC):At the canter and gallop normal horses take one breath matched in time with one stride. This is referred to as respiratory-locomotory coupling. The amount of time taken to inhale is the same as the time taken to exhale. The amount of air moved in and out of the lungs increases in direct proportion to how fast the horses is running. If a horse runs twice as fast it must move twice as much air in and out.
During exercise, when horses inhale, around 90% of the resistance (obstruction) to air movement is in the airways that are in the head, namely, the nostrils, the nasal passages and the larynx. But when horses are exhaling the majority of resistance to air movement (55%) is in the airways within the lung.
A close relationship between limb and respiratory rhythms has been shown in clinically healthy galloping horses due to mechanical constraints in the thoracic region. This synchronisation leads to a 1/1 ratio between stride frequency (SF) and respiratory frequency (RF) during galloping. Very little is known about locomotor-respiratory coupling (LRC) during fast trot.

Equine Sense of Smell (Olfactory Ability)

Equine Sense of Smell: Like most other animals horses have an acute sense of smell which is an important tool which horses make to gather information. As prey animals, horses rely on their senses to an even greater degree than most animals do. Their anatomy has evolved specifically to provide for this protection. Compared to humans’, horses’ nostrils are very large. When flared to gather more scent, equine nostrils funnel aromatic molecules through long nasal passages containing millions of olfactory receptors, just like humans. However unlike human’s horses have another unique tool in their kit of smelling tools and that is a second olfactory or smelling system. Located in all places in the mouth, under the horse’s nasal cavity are the vomeronasal organs (VNO). These tubular, cartilaginous organs are roughly 12 centimeters long and lined with mucous membranes containing sensory fibers of the olfactory nerve. The VNO expands and contracts like a pump with stimulation from strong odors, following their own pathways to the brain, functioning virtually as separate sensory organs. Why two sensory organs when humans get along fine with just one set? The VNO’s purpose is the detection and analysis of pheromones, whose purpose is to indicate another horse’s sexual status. As such, the VNO is also a sexual organ, assisting stallions to identify mares in season.

Although the horses sense of smell is primarily an protective warning tool; smelling predators, fires, approaching storms and soiled forage this is not an exclusive tool list. Horses also use smell as a social tool. Houses greet each other (People to) by smelling. Mares recognize their foals by smell. Stallions mark just about everything by the smell of their urine and feces. Both sexes use their the vomeronasal organs (VNO) (Known as the Flehmen response in stallions and more rarely, in geldings) and provides evidence that smell affects equine behavior, for example to determine breeding information.