Learning About Horses - Smell & Nose

 Learning About Horses - Smell

Horses have a strong sense of smell. Horses can detect each other with just this sense. Horses remember the unique smells of the horses in the herd. These smells remain in the horse's brain for a long time. A horse is able to smell human sweat because of fear or anxiety and then respond accordingly. 

Horses use their sense of smell to identify friends, seek sexual relationships, recognize territory, find appetizing meals, and sense danger. Humans are predators so they are much more vision-oriented. "Horses depend on their sense of smell the way we depend on language."

Dogs have the most sensitive noses but horses are not far behind. 

Horses can smell water and food if it is clean or not. 

Nostrils are designed to take in a greater number of molecules. 

Because humans have such a poor sense of smell and do not understand all the complications that can occur during such research. We do not understand the actual range and acuity of a horse's sense of smell. 

Nasal Anatomy

Horses have long cavernous nasal passages that facilitate the intake of large quantities of air during exercise, as well as all the chemical messages in air. 

Horses olfactory receptors are amazing. They have millions of elongated nerve cells (specialized to analyze smells) located in the mucous membranes in the upper portion of the nasal cavity. When airborne odor molecules come into contact with the lipid and protein material of the mucous membranes, they interact with the microscopic tufts of hair protruding from the receptor cells. When the horse sniffs if can intensify the currents of air in the nasal passages. This provides more contact between the odor molecules and the receptor cells and gives it more time for analysis. 

The olfactory cells send out two branches: One extends over the surface of the olfactory mucosa. One acts as a direct pipeline to the brain. 

The horse has twin olfactory bulbs (distinct areas of the brain responsible for identifying scents). They are located at the very front of the cerebrum - one on each lobe of the cerebrum. They are connected via the main olfactory nerves to the receptors in the nasal passages. The olfactory bulbs are one of the only brain structures that do not cross over. The receptors in the left nostril are connected to the left olfactory bulb. Right is connected to right. 

Horses have TWO olfactory systems

Horses have a second pair of olfactory organs under the floor of the horse's nasal cavity - the vomeronasal organs (Jacobson's Organs). Almost all animals have vomeronasal organs (VNO) EXCEPT humans, cetaceans sea mammals which do not have them. Lots of research has been done with reptiles and rodents but not much for equines. 

VNOs in horses are tubular and cartilaginous and are about 12 centimeters long. Even though they are so big they are carefully concealed. They are lined with mucous membranes. They contain more sensory fibers of the olfactory nerve. They are connected to the main nasal passages by a duct called the nasopalatine duct. Because horses are NOT mouth breathers the VNOs only communicate with the nasal passages. VNOs seem to expand and contract like a pump with stimulation from strong odors. They have their own pathways to the brain. They function almost completely as separate sensory organs. 

VNOs main purpose is the detection and analysis of pheromones, the chemicals signals emanating from other horses. The main purpose of pheromones is to indicate an animal's sexual status. The VNO is a sex organ. VNOs help stallion identify when a mare is in heat and receptive to breeding, when she is out of season & reject his advances, and when there is a rival stallion in the area ready to steal his mares. 

Stimulation of VNOs has a profound influence on the animal's endocrine system. 

"Flehmen" posture is when horse tilt up his head, curl upper lip in a "horse laugh" appears to help horses trap pheromone scents in the VNOs so they can be analyzed more closely. After the horse draws in the organic odor (several seconds of olfactory investigation), he curls up his lip up to temporarily close the nasal passages and hold the particles inside. Then an upward head tilt seems to help the airborne molecules linger in the VNOs. A horse performing a flehmen is giving you an outward demonstration of a stimulated vomeronasal organ. Stallions flehmen the most. Mares will also flehmen will do it smelling the birthing fluids on a newborn foal often triggers the response. 

Horses also flehmen when they come in contact with an unusually strange or pungent inorganic odor-smoke from a fire or fresh paint. 

A horse's olfactory systems never rest. Horses analyze smells every second of the day-barn smells and herd smells, water smells, plant smells, and the smells of the humans, dogs, and cats that enter his environment every day. In a domestic setup, a horse's olfactory senses might be overwhelmed with artificial odors like liniments, fly sprays, and deworming drugs.

Domestic horse's sense of smell is a marvel, capable of identifying his owner at 100 paces, helping to bring him (and you) home from the woods even then the trail has disappeared, alerting him to the presence of yucky medications in his sweet feed even though you've doctored them with applesauce and molasses. 

https://lvperformance.com/blog/facts-on-horses-senses-you-need-to-know/

https://thehorse.com/13971/equine-sense-of-smell/