Stimulating the horse’s senses can improve its movements and posture

The senses work like reflexes to a certain degree, meaning that they work without us being aware of them. However, we can consciously stimulate them, and that’s exactly what ProPrio Training can do for your horse. ProPrio Training is sensorimotor training.

In order for the brain to control the body’s movements, it needs input from all the senses. In this blog, I will give you some insight into the horse’s senses, which all affect the body’s control and maintenance of posture, and body movement. The contents of the blog is an excerpt from chapter 4 of the ProPrio Training book.

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Guide: This is a very long blog entry, but you can always click on the individual senses below and go straight to that section. You can return here by clicking ”Back to the top” in the right hand corner

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All the senses give the horse’s brain the input it needs for coordination and movement

The sight is of great importance to coordination, because distance and depth is judged through the eyes, and it helps our coordination. We feel it when watching a 3D movie. We can become dizzy or feel like we are almost part the movie. The ear is important for balance, because the large organ for balance and equilibrium is inside the ear. The sensory impulses from here, along with the sensory impulses from proprioceptors, give the brain input about where the different body parts are in relation to each other. This keeps the body in equilibrium. When the horse’s sensory nervous system is well-stimulated, the horse can balance and coordinate his movements. The sensory nerves give the brain input from the body about where it is, and with good proprioception, the body knows how to respond. If the horse encounters an obstacle in his path, for example, he can navigate safely around it without falling. Proprioceptors are part of maintaining a good posture and a strong core, from which good balance and coordination follow. With good proprioception and posture, the horse can move safely in the world, biomechanically speaking.
 
 

The sense of sight

The eyes are almost an extension of the brain and they are connected to the brain through the optic nerve. The optic nerve is the second cranial nerve (nervus opticus). It perceives visual impressions and transmits them to the brain. The optic nerve crosses over in the brain. That means that most of what is perceived with the right eye is processed in the left side of the brain, and most of what is perceived with the left eye is processed in the right side of the brain. Information about objects in the surroundings and the body’s position in relation to the surroundings is perceived with the eyes and transmitted to the brain through the optic nerve.

The sense of sight is complex and composed of different parts. There are parts determining the position of objects, their boundaries, size, shape, and lighting. Another part colors the objects, and a third part is especially sensitive to things moving through the visual field.

The horse’s eye is one of the biggest in the animal kingdom, and with its 34 mm in diameter it is almost the same size as that of an elephant. The human eye is only about 24 mm in diameter. Horses can dilate their pupil all the way to the edge of the eye, allowing them to take in a lot of light. This means that the horse’s night vision is very well-developed and about 5 times more sensitive than that of humans.

The horse’s ability to dilate their pupil is connected to the iris (the colored part of the eye) being able to retract very far, making the pupil extremely large, and so the light absorption is great. However, this happens somewhat slower than in humans, because the muscles that regulate the iris in horses are relatively weak. That means the horse needs about twice as long as humans (30-40 seconds vs 15-20 seconds in humans) to adjust from light to dark and vice versa.

The horse’s eyes are placed high up on the long head and on each side of the head. The placement makes it possible for the horse to see 350°, so almost the whole way around them. But they do have two blind spots: right in front of their face in a cone shaped area reaching about 1.25 m in front of them, and behind their neck, an area with an angle of about 10° that covers the whole back and 2-3 m behind them, when the head and neck are pointed straight forward.

The placement of the eyes on each side of the horse’s head means that the horse not only sees binocularly (focusing with both eyes), like humans do, but that horses can see different things with each eye simultaneously (monocular vision). In spite of perceiving two different images at the same time, the horse’s brain is able to decode them.

Forward, the horse has a binocular field of vision of about 65° (where humans have 120°), which is covered by both eyes, and that makes it possible for the horse to judge distance and gives him a more precise perception of distance, shapes, and depth. The horse is not capable of this in the monocular field of vision, which is an area of about 285°.

The horse depends on the ability to move his head to achieve visual focus and judge distance. The horse can only move his eyeballs from side to side, and not up and down like humans can. So it is crucial not to set the horse’s head in a fixed position or posture, but to allow him to move his head up and down and to the sides. Remember this when training your horse.
 
Can your horse see colors?
The horse’s color vision has been the object of many studies, and we don’t have all the answers yet. The anatomy of the horse’s eye shows that it has both cone and rod cells. The rod cells cannot perceive color, but they are around 100.000 times more sensitive to light than the cone cells. The cone cells are the cells in the eye responsible for color vision. Humans have more cone cells than most other animals, and have great color vision, allowing us to distinguish between a lot of different colors.

Horses certainly see some colors, but compared to humans, horses don’t see nearly as many. Evidence suggests that horses struggle to see red and green colors, and they have a hard time distinguishing between yellow and green shades.

However, horses are good at perceiving contrasts, because their pupil allows for so much light absorption. We use this in ProPrio Training by having a black pole on one side of the horse and a white pole on the other in the courses we construct for the horse. In ProPrio Training, the sight is important for the horse when navigating between the poles and across the mattresses in the courses we lay out for them.
 
 

The sense of hearing

The cochlea in the inner ear converts sound waves to neural impulses, and allows the sound’s frequency, volume, and place of origin to be perceived by the horse. In addition, hearing supports the sense of space, direction, and distance.

The vestibular senses
The organ of equilibrium (the vestibular system) is also located in the inner ear. It registers linear acceleration and informs the brain of position and motion of the head in space in relation to the vertical plane. The vestibular system is filled with liquid (endolymph) and its walls are coated in a special kind of receptors called hair cells. The hair cells (stereocilia) protrude into the liquid and detect changes in the liquid. When the head tilts, the liquid moves and makes the hair cells change direction.

This is registered by the brain, which uses the information to determine the head’s position and direction. The vestibular system detects rotational movements and linear acceleration, which helps stabilize vision and maintain posture in movement.

The sense of balance works closely with sight. There is a reflex called the vestibulo-ocular reflex. It controls some of the muscles in the eye and coordinate the movements of the eyes and head. When the head turns, the eyes remain fixed on the field of vision for as long as possible. If the head is tilted to one side, the eyes rotate to the other, and that way keep the field of vision horizontal. Eye movements and control of the eyes is dependent on the vestibulo-ocular reflex and controlled by the cerebral cortex. This again helps the understanding of why it’s so important that the horse always carries his head in front of the vertical plane and is allowed to move his head, instead of being fixated in a certain position.

In ProPrio Training, we therefore never use any kind of side reins or other headsetting aids, and we always train with a loose, soft, and yielding contact on the rein when riding the horse.
 
 

The sense of touch

When the skin is touched, it activates sensory nerve cells, which send a signal to the central nervous system (CNS) located in the spine and the brain, and a signal is sent back to the area. The skin can register pressure, touch, temperature, and pain. Muscles respond to the skin being touched, and some muscles are activated/contracted. So the body will react to stimuli on the skin in the place it occurs, and the body has then learned something about it.

The sense of touch is particularly sensitive to changes in the stimuli and to stimuli that moves across the skin. You can see the sensitivity of horses as they, despite being covered in fur, feel a tiny fly landing on them.

There are many proprioceptors in the skin, and it is to our benefit to activate them before and during ProPrio Training, as well as in the regular daily training. This is done efficiently by stroking the horse’s coat, in the direction of fur growth. Also stroke the legs, down to the coronary band, which is very sensitive to touch. When we train with the ProPrio equipment, the horses like to touch it with their muzzles and paw at it with their hooves before stepping on it. It gives the horse information about the object it’s about to step on.

 

 
 

The sense of smell

The horse’s sense of smell is excellent, perhaps almost as good as that of dogs. In the horse’s nose, there is a maze of cartilage. In the rear part of the nasal cavity’s cartilage, the outer wall is covered in olfactory epithelium (a mucous membrane full of sensory neurons attached to cilia). In the mucous membrane, the sensory neurons interact with odors and transmit the information to the brain via the first cranial nerve (nervus olfactorius) and on to the olfactory bulbs where the smell is analyzed. In fact, the olfactory nerve is one of the only structures in the brain that doesn’t cross over. So all smells from the left nostril are directly processed by the olfactory bulb in the left side of the brain, and vice versa.

In the outermost part of the nose, the horse has the vomeronasal organ (also known as Jacobson’s organ, named for the Danish surgeon Ludwig Jacobson who first described this organ in 1813), which detects a number of specific scents. This organ is comprised of two small parallel passages, located in the hard part of the palate, with an opening to the nostrils which connects the organ to the olfactory nerve in the opposite end.

They use their sense of smell to identify friends, look for a mate, recognize territory, find food, and sense danger. They are quick to sense fear in other animals and people. Scientists are still trying to identify exactly which chemical signals emanate to signal “danger”, but they are fairly certain that horses pick up scents that are produced when other animals and people feel fear.

Scent recognition plays a large part in social relations; for example, orphaned foals are more easily accepted by a foster mare if the foal is rubbed in sweat or manure from the foster mare or covered in the skin of the mare’s own dead foal. Horses also use their sense of smell to examine if their food is good or bad. Horses normally won’t eat poisonous plants or moldy feed. However, some poisonous plants have a chemical composition that makes them irresistible to horses.

Horses always smell each other when they meet for the first time, and they will do the same when they meet a new person or an animal that doesn’t pose a threat. By smelling each other, they get information about the other horse’s status, personality, and mood. A horse that has been separated from its herd can track it by smelling their scents in the grass or in manure. The horse’s sense of smell is so well-developed that it can smell which horse made which pile of manure.

Horses can refine their sense of smell further by stretching their upper lip out and upwards, funneling the scent into the vomeronasal organ. This is called the flehmen response. They do this to gather more information about the new or particularly interesting scent they have picked up.

Stimulate the horse’s sense of smell for mutual benefit
With horses that are nervous or afraid, we can use their sense of smell to help them. For example, the scent of lavender is calming for both animals and people. You can put a small amount of essential oil in both nostrils and achieve a calming effect. When the horse encounters new things, for example the ProPrio equipment, you always have to let them smell it. That way, the horse will quickly discover that it’s not dangerous, and it is safe to work with.
 
 

The sense of taste

The sense of taste is well-developed in horses and just as with humans, the sense of taste is connected to the sense of smell. The horse can taste sweet, salty, and sour and normally avoids eating hay or other feed if it is moldy or of poor quality.

The taste buds, which detect flavor, are primarily located in the horse’s tongue and a few in the soft part of the palate. Taste buds are microscopical ‘clumps’ of cells, papillae, located in the tissue of the tongue. Spit dissolves the feed, and when it is liquid, it seeps into the taste pores where it stimulates the taste receptor cells, which then stimulate the nerve cells. Within the papillae, there are small salivary glands which secrete saliva into the taste pores. This is believed to be cleansing the taste buds, so they are ready to detect new taste. Branches from both the seventh cranial nerve (nervus abducens) and the fifth cranial nerve (nervus trigeminus) receive signals about taste and transmit the information to the brain.

Horses lick and bite things, including the ProPrio equipment when they are introduced to it. It is a way for them to gather more information about the object that we want them to step on.
 
 

Proprioception (the sense of motion)

In humans, it has been shown that the body’s most important stabilizing muscles, those that stabilize the entire spinal column (neck and spinal vertebrae), are trained and strengthened when the proprioceptors are stimulated. The nervous system requires a stable spinal column to function efficiently and stay healthy, because the nerves branch out from the spinal cord at each individual vertebra.

There are 3 kinds of proprioceptors:

Muscle spindle cells: They are located in the deep muscle tissue and detect stretch in the muscles. They send signals to the brain about muscle length and changes of length. When the brain has processed the information, it sends a signal to the muscles, making them contract.

Golgi tendon organs: These are located in the transition between muscles and tendons, and primarily signal the brain about tension in the muscles when they contract. When the brain receives a signal from the Golgi tendon organs, it will signal the muscle to relax.

Joint receptors: They are located in the joint capsules and ligaments of all joints in the body. They are stimulated by mechanical changes in the stability of the joint when the bones change alignment.

Proprioceptors are found throughout the body and send sensory information from the body through the spinal cord to nerve cells in the central nervous system (CNS). When the CNS receives a signal from the proprioceptors, it signals the body how to respond.

The proprioceptors can be seen as the body’s self-defense mechanism. They help prevent bone, muscle, tendon, and joint injuries, if they are well-stimulated. Stimulating these sensory nerves is very important to the body’s balance and coordination. It enables the body to have an understanding of space. With good proprioception, the body is better able to react appropriately, for example know how to navigate an obstacle without being injured.

 
 

Keep an eye on your horse during training

Now you have some insight into the horse’s senses, and how they all influence the horse’s perception of the world, and the things we expose them to. Try to keep it in mind in your continued training and notice how the different senses affect the everyday life and training for you and your horse.