Understanding a Horse's Senses

Horses have a very large eye and a very large pupil.

 The senses are an important part of what makes horses behaviorally distinct. Animals share the five basic senses: vision, audition (hearing), olfaction (smell), gustation (taste) and touch. The senses are the tools that an animal uses to interact with its environment. As such, the senses can be considered starters of behavior.
 There is a temptation to relate human senses to horses, but horses and people have basic differences in how they see, feel, taste, smell and hear their environment. We do not completely understand horse senses, but the things we have learned have greatly added to our horse knowledge. A review of this information can be helpful in understanding horses.

VISION

 Did you ever look at a horse eye to eye? If you have, you probably noticed a few things. First, they have a very large eye and a very large pupil. Second, the eyeball is placed more to the side of the head, which gives horses a wider field of vision.
Predator species, such as dogs and coyotes, have eyes placed toward the front of their head. This narrows their total field of vision but it increases their binocular (using two-eyes) visual field. Binocular vision gives the predators better depth perception and a more concentrated field of vision. Prey species, such as horses, sheep and cattle, have a much wider visual field. With only slight head movement, horses can scan their entire surroundings. If there is a threat, the behavioral response is generally to flee.
 Much of the width of the visual field that horses see is observed with only one eye. This is called monocular vision. When a horse sees an object with its monocular vision, it will tend to turn toward it so that both eyes can see it (with binocular vision), and the ears can better hear it. There is sometimes a brief visual shift as the horse switches from monocular to binocular vision, which sometimes causes an unexplained “spooking” of the horse.

A horse will turn toward an object so that both eyes can see it (binocular vision).

The size of the pupil improves the ability of a horse to pick up movement. The large size provides a built-in wide angle lens effect which is further enhanced by the placement of the visual receptors in the retina. The total effect is better side (peripheral) vision. The horse can see movement very well.

 Does the horse sacrifice visual accuracy to get a wider field of vision? In general, yes, but the answer to the question is not clear. Current thought is that, while the horse sees practically all the way around its body, the image is not as clearly defined as what humans see, especially within four feet. This, plus the fact that a horse cannot see directly below its head, may explain why horses often raise their head to observe close objects. Conversely, a horse tends to lower its head to observe faraway objects.

 In spite of the wide field of vision, there is a “blind spot” directly behind the horse. People should avoid approaching a horse from behind, because their presence may not be detected until they are close, and this could startle the horse. Some horses may instinctively kick in this situation. If approaching a horse from the rear cannot be avoided, make a soothing noise to announce your presence. Do not “sneak up” on a horse from behind.

 Another question often asked is do horses have color vision? For many years it was believed that both horses and cattle were color blind. If horses can distinguish colors, it is unlikely that horses’ ability to see color is equal to other species, such as humans.

HEARING 

 In spite of its importance, there is limited information about the auditory (hearing) sense of horses. We know horses are sensitive to high-pitched noises and the release of stress-related hormones in response to sudden loud noises such as firecrackers or barking dogs.

A horse can rotate its ears independently from front to side to pinpoint a sound.

Horses become nervous and difficult to handle when stress hormones are elevated, so it may be useful to avoid loud or shrill noises when handling or moving horses.
 The horse can amplify and pinpoint sound with its ears. Sound arrives at each ear at slightly different times, which allows the horse to use sound as a means to tell where the sound came from.
 The horse can then move its ears, head or its entire body to tell more about the source of the sound. This skill is probably as important as sight and smell for keeping the horse, as a prey species, alive.

SMELL

The horse’s sense of smell (olfactory) may be the most difficult for humans to understand. Horses have a more highly developed sense of smell than humans, and they use their ability to distinguish different odors more in their everyday lives.

  Horses use their sense of smell in a number of ways. Horses use smell to identify other horses, particularly when a mare uses smell to pick out her foal from a group. Another common use of smell is during mating. The stallion constantly checks mares to detect the ones in heat (estrus). The classic head-raised, lip-curling behavior of the stallion (bulls and rams, also) as he smells females is called the Flehmen response. This trait, which may be occasionally observed in females, is due to a special organ (vomeronasal organ) above the roof of the mouth, which humans do not have.

 Horses probably use their olfactory sense to locate water and identify subtle or major differences between pastures and feeds. Smell also triggers behavioral responses. There are, for example, horses that do not like the smell of tobacco smoke or may react negatively to the odor of certain medications.

The raised-head, lip-curling behavior usually displayed by stallions during mating is called the Flehmen response.

  Some people believe that horses can sense when a person is afraid — which is probably true — and this is often referred to as horses’ ability to “smell fear.” It is possible that the horse can smell some small change in the fearful human, but it is equally likely that the horse can sense the human nervousness via other senses.

   Horses will use their sense of smell to select fresh feed in preference to spoiled feed. The next time you are tempted to dispose of moldy feed or hay by feeding it to a horse, try smelling it yourself. Then remember, if it smells bad to you, it may smell worse to the horse. (This may not always work, however, because some molds, such as highly poisonous aflatoxins, cannot be detected by humans.)

TASTE

  The sense of taste in horses is probably not as important as the sense of smell, and it is difficult to separate behavioral responses that are due primarily to taste from responses caused by the olfactory sense. Using their sense of taste, however, is part of why horses can tell one feed from another. When presented with a variety of feeds, horses will select certain feeds over others. In practical situations, such as under grazing conditions with multiple forage species present, the horse will select different types and species than either sheep, goats or cattle.

Horses enjoy special treats, such as carrots or alfalfa cubes.

  There have been experiments to determine if animals have “nutritional wisdom.” This is based on the premise that horses will attempt to eat feeds that provide them with the nutrients needed. In most cases, however, horses are unlikely to balance their own ration when provided a variety of feeds. If possible, they will consume feeds at a level far higher than necessary to provide essential nutrients. For example, salt is often provided to meet horses’ requirement for sodium; however, horses will often consume many times the amount of salt needed to meet the requirement. Fortunately, there is no evidence that over consumption of salt will cause health problems if adequate water is available.

TOUCH

 The sense of touch is certainly well developed in horses, and is one of the most important senses in terms of human interaction with horses. The nose, lips, mouth and possibly the ears are the most sensitive areas to touch and, consequently, most readily lend themselves to feeling behavior. Although hooves do not respond to touching, they should not be regarded as without feeling. In fact, various parts of the hoof are able to feel touch, as anyone who has shod horses or trimmed hooves can relate.

 Other areas of the body are also sensitive to touch. The flanks for example, are particularly sensitive, and can pick up a light signal from the rider. The ribs are also sensitive, as are the withers and back.

 Understanding the degree to which horses are sensitive to touch can be valuable to the trainer. For example, knowing that horses can feel the slightest touch with their lips underscores the importance of developing “a light touch” on the reins, and making certain that bridles be correctly fit to the horses head and mouth. Knowing that the horse can feel the slightest shift of weight in the saddle illustrates why the rider’s position is important as the mount is guided toward a jump or other maneuver. Poor position, exaggerated movement or excessive force are confusing to horses and result in poor performance.

  The sense of touch is undoubtedly important in interaction between animals. Foals seek bodily contact with their dams (mothers), and mares respond to the touching behavior of their foals in various ways, including milk let-down in response to the nuzzling/suckling stimulus of foals.

  Another example of horses’ sensitivity to touch is related to electric fences. Anyone who has used electric fences with a variety of grazing animal species knows that horses are very sensitive to electricity. To use electric fences with horses, the wire should be placed approximately at nose height. High-quality, well-grounded chargers should be used, and horses should be trained to the fence by introducing them to a well-constructed permanent electric fence for their first experience.

Related Article : The Role of the Senses in Training