Senses: Vision
Senses
The animals perceive their surroundings through their senses. Vision, hearing, and feeling give important information about the animals’ surroundings, and play an important part in the communication with other animals and humans.
The senses are significant for how our production animals experience being at the slaughterhouse or to be killed.
Vision
Vision gives the animal valuable, detailed information about the surroundings, i.e. various types of threats or the whereabouts of the herd.
The wild ancestors to our production animals constantly had to to keep watch for predators, a behaviour that remains with the production animals today. They are, minks excluded, prey and react quickly to danger, i.e. sudden movements, by fleeing. Vision is very important for the animal to be able to detect a predator in time. This is reflected in how the eyes placed. The eyes are placed laterally on the head, usually between 300 to 330° (the human field of vision is 180°).
The extensive panorama viewing depends on the animal being able to notice different views with each eye. The animals have stereopsis and can estimate distances in a limited area straight forward where the fields of vision are overlapping.
There iscan angle backward, The backward area, and possibly also forward, where the animal cannot see as a consequence of how the eyes are placed (that is, where the animal’s body and i.e. ears conceal the view).
To be able to see in the blind zone, the animal has to turn its head/neck sidewise.blindzone, where the animal does not see anything when the head is hold straight forward.
You can read more about the importance of vision for slaughter and killing in the module Handling.
Equine and bovine animals
Equine and bovine animals have limited ability to alternate between short distance and long distance vision. They have to look straight at an object to see it clearly and to be able to make distance estimates. These limitations may explain why the animals hesitate or avoid foreign elements in their way.
The animals must lower their heads to clearly see objects on the ground directly in front of them. This makes it more complicated for the animals to walk down i.e. a ramp. It takes a while for the eye to adjust so that the the animal can see clearly at a close distance.
Equine and bovine animals experience light contrasts and some colour vision. They have a fairly good vision in the dark.
Light from different objects in the surroundings is focused by the lens on the retina which transmits nerve signals to the brain where the image is interpreted. Drawing: Anne Larsen, SLU.
Even if there are some differences among the production animals, the eyes still have similar build and function. Incoming light from the surroundings reach sensory cells on the retina, which transmits information to the brain, where the image is interpreted.
Production animals (except minks) have a good overview (yellow), have stereopsis and can evaluate distance in a limited area forward (blue) and see nothing at all in a limited area behind when the head is hold straightly forward (grey).
Illustration: Sofia Wiberg, SLU.
Estimating distances
Cattle see movements better than standing objects. It is easier for them to see an animal that is moving hundreds of metres away than an object, i.e. a branch or other protruding object, at close range.
Cattle are considered to have difficulties to focus and estimate distances, which would explain why they, often without evading, can rush straight against a wire or chain while evading a more visible fence.
This can also explain why they evade shadows as if they were physical obstacles.
Photo: Anne Larsen, SLU.
Pigs do not have well developed vision. They have limited vison at long range. Pigs do probably detect moving objects easier than standing. Photo: Guiseppe Vezzoli
Photo: Kristina Johansson.
Horses raise their head to be able to see distant objects clearly, and lower it to see close objects clearly.Horses can detect very subtle changes when an object is focused, i.e. movements in the face and the position of the ears of another horse.
Except for the blind zone backward, horses do not see an area just in front of the muzzle. Therefore, the horse does not see what it is eating while feeding, and may not detect a hand that is lead to the muzzle or the mouth.
Horses have good vision in the dark.
Sheep are regarded to have good vision both at close and distant range. They see movements better than standing objects.
Sheep are regarded to have difficulties to focus and estimate distances, which would explain why they, often without evading,
can rush straight against a wire or chain while evading a more
visible fence.
This can also explain why they evade shadows as if they were physical obstacles. Vision can be limited the amount of wool and
the horns and the ears. An animal with a limited field of vision is
more easily scared.
Photo: Jan Svedberg.
The animal can see the personnel? Photo: Jan Svedberg.
The animal can see the personnel?: Kristina Johansson
Remember!
- Equine and bovine animals have an extensive field of vision, mainly for detection of danger.
- The animals have limited ability to estimate distances.
- They have to look straight at an object to see it clearly.
- They have limited vision downward and cannot see anything straight backward.
Field vision of poultry.
The bird can see the personnel!
True
False
For birds, vision is better developed and the eyes are relatively bigger than
for equine and bovine animals. Poultry, like other birds, have sharp vision
and can quickly adapt from short distance to long distance viewing.
By moving the head rapidly from side to side, stereopsis and distance estimating are facilitated.
Poultry experience light contrasts and a broad spectrum of colours. It is on the other hand known that chicken and turkey do not have good night vision. Except for the blind zone backward, they also do not see an area just in front of the beak.
Hens (includes the species hens if the breed is not specified) can focus at very small particles within five metres, while larger objects, i.e. a predator can be detected at ranges up to 50 metres. Photo: Stefan Gunnarsson, SLU.
The bird can see the personnel? Photo: Viveca Sandström, SLU.
The bird can see the personnel? Photo: Viveca Sandström, SLU.
Remember
- Poultry have an extensive field of vision, mainly for
detecting danger. - They have sharp vision.
- They have well developed colour vision.
