Description and Physical Characteristics of Horses

Horses generate considerable heat during exercise. They lose heat primarily by evaporative cooling (usually sweating), just like people do. However, because sweat does not readily evaporate during hot, humid weather, evaporative cooling becomes ineffective under these conditions. During hot, sticky summer days, exercise should be limited to avoid heat stress. Heat stress and continued exercise can lead to dehydration and eventually shock. Adequate water, proper diet (including vitamins and minerals), and limits on exercise are all needed to avoid heat stress.

Horses are large, bulky animals that are good at conserving heat during periods of colder weather. Regardless, they still need adequate shelter, diet, water, and routine veterinary health care to prevent wintertime problems ( see Providing a Home for a Horse).

The primary sensory input in horses is sight. The importance of vision is reflected in the size of the equine eye, which is the largest of any land mammal, and by the fact that the visual cortex of the equine brain handles one-third of all sensory input.

Horses’ eyes are set on the side of the head, rather than facing front as in people, dogs, and cats. This gives them extraordinary peripheral vision, which is useful for animals (for example, rabbits and most birds) that must constantly watch for predators. Horses can generally see over a 340° arc without moving their heads, with only small blind spots directly behind and in front of them. These blind spots are caused by the body of the horse (behind) and the large forehead and muzzle (in front) obstructing the horse’s vision. Horses step slightly to the side to see things behind them, and back up and lower their head to see directly in front.

Vision range, horse

Horses see a panoramic view as a form of monocular vision, which means that each eye is viewing images independently. These images are transferred to a band of retinal cells called cones within a “retinal streak.” A second group of cones provides binocular vision in an arc of 55 to 65° in front of the horse. The relatively large number of cones enables horses to see distinct images better than dogs do but not quite as well as people can. These cones also mean that horses have some color vision. Horses also have a large number of rods, which are the specific type of cells in the retina responsible for night vision, as well as the reflective tapetum lucidum, which is also found in both dogs and cats. For this reason, horses see considerably better in the dark than people, and even cats. Horses also share the protective third eyelid that is found in both dogs and cats ( see Sight).

Because horses rely on monocular vision, they have poor depth perception. They can misjudge the depth of a small puddle or the distance to a fence. Horses compensate for this by comparing the size of an object to their memory of what they have seen in the past. For example, if a person or fence appears smaller, then it must be farther away. A horse will lower its head to judge closer distances and raise it to judge objects farther away.

In general, horse vision is a little blurrier and a little less colorful than human vision. However, horses see movement very well throughout the 340° arc of their peripheral vision. This is why horses may “spook” when confronted with even minor changes around them—another useful survival skill for herd animals.

As horses age, their vision may worsen. Unfortunately, there are few medical treatments for poor sight in horses. However, watching for signs of poor vision can help prevent injury to both you and your horse.

Horses have large ears that are good at magnifying sound and noting its direction. Each ear can swivel independently up to 180°, allowing horses to locate multiple sounds at the same time. The ears also provide clues to a horse’s emotional state. For example, a horse with ears that are laid back may be indicating aggression, pain, or fear (such as in response to a loud or unfamiliar noise).

In general, horses hear slightly better than people do and are able to hear sounds at both higher and lower frequencies. Horses are good at hearing the high-pitched squeaks or crackles associated with the stealthy approach of a predator.

Horses experience age-related hearing loss, which means that older animals may not hear your approach as well as they did when younger. Spooking can be avoided by making sure that your horse can see you or knows you are approaching. Hearing loss can also be caused by ear infection or by a mite or tick infestation, so you should ask your veterinarian to periodically check your horse’s ears.

In addition to providing information about the world in general, the sense of smell is the primary way that horses recognize each other as well as people. For example, horses exchange breath on meeting, and stallions assess the sexual status of a mare through scent. The equine nose has a large internal surface area that contains many chemical receptors within the mucous membrane. The surface area devoted to scent detection is many hundred times greater than in people, again highlighting the importance of the equine sense of smell.

Horses enjoy their food through the sense of taste. Taste buds are located on the tongue, the soft palate, and the back of the throat. It is not known whether horses have the 4 -basic types of taste (sweet, sour, bitter, and salty). However, it is known that they can at least distinguish salty and sweet. In fact, like people, horses are known to have a sweet tooth, appreciating such things as apples, carrots, and honey. Horses are also known to tolerate substances (including medications) that people generally find very bitter.

The equine leg is designed for rapid movement over a variety of surfaces. The upper part of the leg is heavily muscled, while the lower part acts as a springboard to enhance the stride. The leg is supported by a suspensory apparatus of tendons and ligaments. The tendons, which can be felt along the back of the lower leg, run the length of the limb, while the many joints are held together and protected by ligaments and joint capsules. Horses also have a unique anatomical feature called the stay apparatus, which allows them to “rest” a rear leg while standing on the other 3 for prolonged periods. This is why horses can sleep standing up.

Horses walk and run on their hooves. The cannon and splint bones are in the lower leg, while the pastern bones are between the fetlock and the hoof.

The long, lean, flexible equine leg is excellent for its purpose, but it is also delicate and easily injured. The tremendous amount of weight that is balanced on the hooves and lower limbs make these areas particularly subject to injury.

The hoof consists of a wall of horny keratin (a protein) that grows down from a band called the coronet at the top of the hoof. This process is similar to the way our fingernails grow out from the cuticle. The sole of the equine foot is concave, with a resilient wedge of tissue called the frog that juts forward from the heel. Inside the hoof is the coffin bone (which is shaped like the hoof) and additional resilient tissue. The sole and the frog protect the underside of the foot, while the resilient tissues cushion each step like a spring ( see Figure: Horse hoof).

Limbs, horse

Horse hoof

Because the hoof is subjected to tremendous, repetitive impact, it can develop numerous problems that lead to lameness, including bruises, infections, hoof rot, and a serious inflammation in the area of the coffin bone and coronet called laminitis. Therefore, hoof care is an important part of equine husbandry and preventive medicine.