With Ipos Technology’s products, we try to bring objectivity and science to horse sport. We have discovered some other interesting things that can be measured that also influence welfare and performance of horses. The Netherlands is one of the most densely populated countries in the world. When it comes to animal density, it also scores very high, with more than 100 million animals. The result of this is that humans and animals live very closely together, and sometimes disturb each other. For humans, noise nuisance is a familiar problem as a cause of stress and insomnia. But what about horses? Do they experience noise nuisance as well?
Horses are ‘flight animals’. They originate from steppes, which are an open landscape, where very few noises occur. Loud or many noises aren’t something horses naturally know. Horses started living near humans, only 6,000 years ago, which means that they haven’t had a great deal of time to adjust to human, genetically. In terms of behavior and instincts, they will still closely resemble their ancestors on the steppe.
This life as a prey animal on wide plains has made that the horse always keeps a sharp eye and ear on its environment. By nature, horses distrust every change at first, until they learn that a stimulus, like a sound, is not dangerous. This ancient instinct still determines the way that horses respond to sounds, and how much it bothers them.
The range of a horse’s hearing starts at 5-15 decibel (dB), which is a little higher than a human’s. We can detect sounds from 0 dB. This means that horses hear very soft sounds after humans. For humans, sound levels above 120 dB start to feel uncomfortable inside the ear. And sound levels between 130-140 dB cause pain. Unfortunately, we cannot ask horses, what it’s like for them, so this kind of ceiling values are not (yet) known for horses. When we’re talking about noise nuisance, not only the intensity of the sound is of importance, but also its duration.
Each new sound will evoke a panic reaction at first. This varies from suddenly lifting the head to turning and bolting, possibly combined with kicking towards the alleged danger. This can result in dangerous situations for caretakers and riders. A horse will get startled more easily from a sound when there is also a visual, than from just a sound alone.
For horses, it is important that they can see each other, and preferably touch each other as well. A horse that is startled will immediately run towards other horses, because of its herd instincts - stronger together. This means that a horse that is alone will get startled more easily, and doesn’t sleep and eat as much in a noisy environment. Alongside this, horses learn which things are frightening, and which are not from each other.
Horses can get used to certain types of background noise. To get accustomed to the sound, it should never be followed by an unpleasant experience or flight response. Preferably, the noise is constantly present or predictable, as to when it will occur. For example, a horse will get used to the sound of a train more quickly when it passes at regular times than if it only occurs every once in a while.
As a guideline, the habituation process of a horse takes between three days and two weeks. This depends very much upon the horse’s previous experiences with the type of noise. In a study with horses that were first kept in a stable and then outside 24/7, the horses slept less for the first three days. After that, the number of hours that they slept stabilized again.
Horses rarely become used to sounds above 100 dB. In a study among wild animals in the United States (including wild horses), the animals could not get used to noises above 100 dB. The animals became frequently startled and ran away from such loud noises. Several other studies with less loud noises around horse stables demonstrate habituation.
We’re assuming that the habituation, just like conditioning horses, is very context-dependent. This means that horses that are used to the sound of a plane, will not immediately be used to the sound of a race track.
In Australia, the organizers of a music concert held near a horse stable were asked to keep the event to a maximum sound norm of 65dB. The horses were not yet used to this kind of sound, and they were very restless on the day of the concert. In particular, the horses in the boxes closest to the concert were tense and ate less. Impulsive changes in the music caused the biggest reaction in the horses.
In a study with horses on several race tracks, noise levels of 51-70 dB have been measured, that the horses barely responded to. They were probably used to these noise levels.
During a study on horses kept in pastures directly underneath the landing strip of Christchurch (United States), noise levels of over 90 dB were measure while a plane was flying over. These horses were also clearly used to the noise, because they showed little to no changes or disturbances in their behavior, and they calmly continued grazing.
Effect of noise on sleep
It is not known to what extent horses might develop a sort of internal tension when they are kept in a noisy environment. In all mentioned studies, there was a period of relative calmness during the night, without races or airplanes, so the horses could sleep during that period.
Like humans, horses know a deep form of sleeping, called the paradoxical sleep. For humans, this is referred to as REM sleep. This deep form of sleeping only occurs in horses when they lie down. Approximately 17% to 25% of the total sleeping time of horses, (three to five hours a day) consists of deep sleep. Horses sleep for short periods of time, several times a day. A horse's deep sleep period normally lasts between 4 minutes and 4.8 minutes. Horses sleep the most between midnight and early in the morning, probably because this is the calmest time. Noise and commotion in their environment shorten the deep sleeping time. This affects the horse’s wellbeing, immune system and performance.
There haven’t yet been any specific studies on the exact sound levels that affect horses’ sleep. For humans, who are not flight animals, of course, the US Environmental Protection Agency has set a maximum of 45 dB to protect them from sleeping interference. For a flight animal like a horse, at least the same norm should be applied.
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