The horse’s sensory world

Thanks to his large eyes with horizontal pupils, and thanks to his retina, with a larger number of cells along a horizontal strip, the horse has panoramic vision on a horizontal visual streak. The rider must therefore be careful, as some of his gestures (hand movement, removing an item of clothing when on horseback) can startle the horse by appearing suddenly in his field of vision.

The optical axis of the eye is deviated 20 % when lowered below a horizontal line. The position of the neck is therefore important : the neck needs to be raised for distance vision, and lowered or tilted for close up vision.
The horse has good vision with little light, he can see movement, and contrasts (sensitivity), but does not see detail quite as well (sharpness). The pupil closes relatively slowly when exposed to light, which means that the time to adapt between light and dark and vice versa, takes some time (e.g loading into a shaded trailer on a sunny day, coming out of a dark stable into a bright sunlit area…). The horse is very sensitive to light contrast.
We now know that the horse can distinguish different colours, even if his perception is different to that of a human being. More specifically, the horse can differentiate between blue, yellow, and white, but green and red on the other hand are not distinguished.

A horse’s ears are more developed than ours with a large funnel. They are very mobile, which allows them to locate the source of a sound.
The horse’s hearing range is quite close to Man’s. He can perceive sounds with a frequency situated between 55Hz an 33500Hz, whereas man hears sounds within a 156Hz to 20000hz range. Horses can hear ultra sounds, inaudible to Man, but can’t hear some bass sounds which Man can perceive.

The sounds that the horse hears best are in the 125Hz to 30000Hz, a range which includes a man’s voice (conversation : 100 to 150Hz, song : 65Hz to 400Hz), a woman’s voice (conversation : 200Hz to 300Hz, song 200Hz to 1500 Hz) and a child’s voice (conversation 300 to 450 Hz).

A horse’s tactile sensitivity is variable depending on the parts of the body and on individuals.
Lips and vibrissae (coarse whiskers around the muzzle) are very sensitive and allow the horse to identify objects and food before grasping them. The vibrissae should never be cut as this deprives the horse of part of his sensory capacities.
Superficials, skin muscles enable the horse to twitch his skin to chase off insects.
The sense of touch is also very important for the horse to form affinities and relaxed relationships with other horses. The withers, a favored scratching zone, is also sensitive.
Touch is also important between horse and rider as contact areas are the basis of communication on which riding is established. Depending on individuals, sensitivity is more or less strong, meaning that response to the rider’s aids can be very variable.

It would seem that sense of smell plays an important rôle in horses : frequent behaviour where a horse inhales the environment (especially urine and droppings), other horses ( a mare with her  foal at birth, a stallion with a mare, horses with each other), a stallion’s behaviour when marking (urine and droppings), nostril conformation and the olfactive mucous lining, suggest that this sense is essential.
The horse also has a vomeronasal organ (also known as Jacobson’s organ) at the base of the nasal cavity. During Flehmen, air is directed from the mouth towards this organ via a small canal. Scientists today think that this olfactive organ is sensitive to pheromones but also to scents.

This sense is linked to the sense of smell and is still open to a wide field of study. The horse has taste receptors or taste buds which enable him to distinguish between sweet and salty, bitter and sharp. Taste sensitivity varies from one individual to another.
At pasture, a horse has a wide range of tastes to choose from. When stabled he is often subject to feeding monotony ; it is therefore of interest to stimulate and enrich the horse’s environment by introducing new tastes. You can for example, give different types of hay, flavour the horse’s ration, offer different feeds for the horse to rediscover the food search behaviour he would have in a field.