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- How do we know if animals experience pain?
How do we know if animals experience pain?
Pain is a sensation of something hurting, and the concept assumes that the affected individual can communicate this. In animals, behaviour and physiology can reveal pain.
Not everyone subjected to something hurtful experiences pain in the same way. Pain is an individual experience and, if others are to know about it, the one affected must tell or indicate by some other means that he or she has pain. Presumably the same applies to animals, but since animals cannot communicate directly with us it is impossible to know with certainty how they experience pain.
Animals can show pain in many ways. They can become inactive, curl up, and cease grooming themselves. Some animals become aggressive and others, e.g. rats with joint inflammation, squeal when touched. Animals with neuralgia (nerve pain) often develop a different gait pattern as they try to avoid putting pressure on the painful area. An important way for researchers and animal handlers to assess pain is to monitor the animal’s body weight. Rodents have a high metabolism and must eat frequently. When they do not feel well their weight decreases rapidly.
Before starting an animal experiment, researchers and veterinarians should decide how to appraise any pain caused by the experiment. By creating score sheets to rate various symptoms and behaviours in animals it is often possible to appraise an animal’s pain objectively. The animal’s suffering can be considered excessive once it reaches a given score, determined prospectively. At that cut-off point the experiment can be stopped, often by putting the animal to death.
Painful stimuli can cause different levels of reaction in the nervous system: pain reflex, pain sensation, and suffering. Read more:
However, animals’ physiology and behaviour can provide indications that they have pain. When an animal does not act normally, researchers and animal handlers must assume that it feels pain. Three criteria can provide guidance:
- The animal has a pain transmission system similar to that in humans. Most animals have some form of pain receptors, and like humans many animals have brain structures that allow them to experience pain.
- The animal is receiving a treatment that is painful for humans, causing a pain response in the animal. For instance, blood pressure or stress hormones could become elevated. The pain response could also cause the animal to behave abnormally.
- The animal is receiving an analgesic that is effective in humans and lowers the pain response.
Varying behaviour
Animals can show pain in many ways. They can become inactive, curl up, and cease grooming themselves. Some animals become aggressive and others, e.g. rats with joint inflammation, squeal when touched. Animals with neuralgia (nerve pain) often develop a different gait pattern as they try to avoid putting pressure on the painful area. An important way for researchers and animal handlers to assess pain is to monitor the animal’s body weight. Rodents have a high metabolism and must eat frequently. When they do not feel well their weight decreases rapidly.
Cut-off point
Before starting an animal experiment, researchers and veterinarians should decide how to appraise any pain caused by the experiment. By creating score sheets to rate various symptoms and behaviours in animals it is often possible to appraise an animal’s pain objectively. The animal’s suffering can be considered excessive once it reaches a given score, determined prospectively. At that cut-off point the experiment can be stopped, often by putting the animal to death.
Three levels
Painful stimuli can cause different levels of reaction in the nervous system: pain reflex, pain sensation, and suffering. Read more:
Text: Karin Nordin
References
- Michael Axelsson, professor in zoology, Göteborgs university.
- Patricia Hedenqvist, veterinarian, Biovitrum AB
- Klas Abelson, research assistant, Uppsala university.
Responsible for content: Mats Ulfendahl, Secretary General of Medicine and health, Swedish Research Council.
Editor: Peter Tillhammar, Swedish Research Council. Contact: Send email to the editorial staff.
Editor: Peter Tillhammar, Swedish Research Council. Contact: Send email to the editorial staff.
