Hearing
Among our domestic animals, hearing is above all important for the animal’s contact with other animals in the herd, and between mother and offspring, but it also has importance for detecting dangers
Sound waves are collected by the outer ear and led through the ear canal and eardrum to the middle ear. The oscillations of the sound are lead by the ossicles (poultry have one) to the inner ear. The sensory cells of the inner ear send nerve signals to the brain where the sound is interpreted.
Birds have no outer ear, but otherwise the ears of production animals have similar build and function. Sound waves are caught by the outer ear and led by the middle ear to the inner ear that sends signals to the brain where the sound is interpreted. There are three components that affect how it is perceived by the animal: direction, frequency and loudness.
The animal detects the direction of the sound by one ear receiving the sound before the other, and with slightly more loudness. The diiference between the ears makes it possible tp determine the direction.
Drawing: Anne Larsen, SLU.
Animals have different abilities to perceive sound frequencies (pitches). Sound frequencies are measured in oscillations per second, Hertz (Hz). A high frequency is perceived as a bright sound and a low frequency as a dark sound.
Loudness is measured in decibel (dB). Decibel is measured on a logarithmic scale, where each doubling of the loudness corresponds to an increase by 3dB. A loudness of 70dB is therefore twice as strong as one of 67dB. When the sound is strong that the animal perceives it as disturbing (not desirable) it is said that it is subjected to noise. Prolonged and transient, repeated noise that the animal cannot escape causes stress. Stress is perceived as discomfort, can deteriorate health, and in the long run also impair growth. Noise therefore leads to worsened animal welfare. Also, sudden and strong unexpected noises can be unpleasant for the animals or frighten them, and in that way increase the risk of injuries.
Equine and bovine animals
Equine and bovine animals generally have good hearing and can perceive frequencies that humans are not capable of hearing. The animals can therefore be frightened by sounds that humans do not perceive. They are most sensitive to sounds at different sound frequencies. I.e. are cattle and pigs most sensitive at 8000Hz and horses at 2000Hz (compared to man: 1000-3000Hz). That means that a sound level at this frequency does not have to as high to be perceived as noise by the animal.
| Species | Approximate hearing range |
| Cattle | 23 – 37000 |
| Pigs | 42 – 40500 |
| Horses | 55 – 35500 |
| Sheep | 125 – 42000 |
| Goats | 78 – 37000 |
| Man | 20 – 20000 |
Hearing range, that is, the lowest to the highest frequency that can be perceived by different species and humans. Compiled from Heffner H.E. 1998. Auditory Awareness, Appl. Anim. Behav. Sci. samt Sjaastad Ø.V., Hove K. och Sand O. 2003. Physiology of domestic animals.
At a slaughterhouse animals are subjected to noise from the environment, i.e. clatter and pounding sounds (sudden, short sounds that can be very strong) from gates, ventilation sounds, and loud voices, but also from the animals when they vocalise because of i.e. fear and anxiety. The animals become more stressed by sounds they are not used to. Consider that even if you are used to the sounds at the slaughterhouse, they are new to the animals!
Noise can be avoided by adjusting the interior and equipment, changing routines, and careful handling of the animals. You will learn more about what can be done to avoid that the animals are subjected to noise at the slaughterhouse in the module Handling.
Pigs for fattening are regarded as the farm animal that is the most sensitive to noise-induced stress. Photo: Bo Algers, SLU
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Horses can move their ears independently from one another, and therefore they can be angled up to 180° to detect where the sound comes from. This is of importance to discover predators in time, but also to know the whereabouts of the rest of the herd.
Remember!
- Equine and bovine animals can perceive higher frequencies than humans, which makes them easily frightened by sounds that humans cannot perceive.
- Noise leads to stress and impaired animal welfare at the slaughterhouse.
- The animals are more affected by sounds they are not used to. Take into consideration that the sounds at the slaughterhouse are new to the animals!
Photo: Anne Larsen, SLU.
Hearing is important particularly for communication. Generally speaking, poultry do not have as good hearing as equine and bovine animals, and cannot perceive sound frequencies as high as they can. They are most sensitive to sounds at specific sound frequencies, i.e. turkeys and ducks at 2000Hz (compare with man: 1000-3000Hz). That means that a sound level at his frequency does not have to be as high to be perceived as noise by the bird.
| Species | Approximate hearing range (Hz) |
| Hens | 15 – 10000 |
| Turkeys | 200 – 6000 |
| Ducks | 100 – 6000 |
| Humans | 20 – 20000 |
Hearing range, that is, the lowest to the highest frequency that can be perceived by different poultry and humans. Compiled from Ekesbo I. 2011. Farm animal behaviour. Characteristics for assessment of health and welfare samt Sjaastad Ø.V., Hove K. och Sand O. 2003. Physiology of domestic animals.
Remember
- Noise leads to stress and impaired animal welfare at the slaughterhouse.
- The animals are more affected by sounds they are not used to.
Take into consideration that the sounds at the slaughterhouse are new to the birds!