What's the noise limit for horses?
Updated: Jun 1, 2019
With IPOS products we try to bring objectivity and science to the sport. We came across some other interesting things that you can measure which also influence welfare and performance of the horses. The Netherlands is one of the most densely populated countries in the world. When it comes to animal density, we’re also scoring 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 and originally live on wide steppes. An open landscape where very few noises occur. Loud or many noises aren’t something horses naturally know. Only 6000 years ago horses started living near humans. This means that the horse genetically haven’t had much time to adjust to humans. 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 his environment. He distrusts every change at first, until he learns that a stimulus, like a sound, is not dangerous. This ancient old instinct still decides the way horses respond to sounds and how much it bothers them.
The range of a horse’s hearing starts at 5-15 decibel (dB), a little higher than a human’s. We can detect sounds from 0 dB. This means that horses hear very soft sounds a little later than humans. For humans sound levels above 120 dB start to feel uncomfortable inside the ear. Sound levels between 130-140 dB are felt as 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.
For horses it is important that they can see each other and preferably touch as well. A horse that’s startled will immediately run towards other horses, because you’re stronger together. This means that a horse that’s alone will get startled more easily, and doesn’t sleep and eat as much. Besides that, horses learn from each other which things are scary, and which are not.
Horses can get used to a certain kind of background noise. To get used 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 pops up every once in a while.
As a guideline you could say that the habituation process of a horse takes between three days and two weeks. This depends severely on previous experiences with the kind of noise. In a study with horses that were first kept in a stable and then outside 24/7, the horses turned out to sleep less for the first three days. After that the amount of hours sleeping stabilized again.
Horses can hardly get used to sounds above 100 dB. In a study among wild animals in the United States (including wild horses) it turned out that the animals could not get used to noises above 100 dB. The animals kept getting startled and running away from such loud noises. Several other studies with less loud noises around horse stables have shown 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 organization of a music concert near a horse stable was asked to keep to a maximum sound norm of 65 dB. These horses were not yet used to this kind of sound and they were very restless on the day of the concert. Mainly 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 (U.S.), 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 kept on grazing.
Effect of noise on sleeping behavior
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 also called the REM sleep. This deep form of sleeping only occurs in horses when they lie down. About 17% to 25% of the total sleeping time, 3 to 5 hours a day, consists of deep sleep. Horses sleep for short periods of time, several times a day. A deep sleeping period normally lasts between 4 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 wellbeing, immune system and performances.
There haven’t 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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