Pain in animals

According to Manfred Zimmermann, an aversive sensory experience can be described as pain perception in animals ,

“Which is triggered by actual or threatened injury, induces motor and vegetative protective reactions, leads to learned avoidance and possibly changes species-specific behavior, including social behavior.”
– Zimmermann, How do animals feel pain?

This definition follows that for the perception of pain in humans, which is described by the International Society for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with, or in terms of, actual or threatened tissue damage.” However, it is not possible to find out whether such an emotional experience also occurs in animals. Therefore the reference to emotional experiences is usually excluded in the definitions of pain perception in animals.

The standard measure of pain in a person is his own statement, because only he knows the quality and intensity of the pain and the degree of suffering. Animals without the ability to speak cannot communicate their condition. Whether they are aware and able to suffer has been the subject of much debate after students were taught until the 1980s that animals would feel no pain.

There are two crucial components to pain: the sensory component ( nociceptor ) and the aversive, negative affective state. The nociceptor enables the detection of harmful stimuli and the subsequent knee-jerk reaction to move the whole body or part of it away from the source of the stimulus. This property can be observed in all large taxa . Nociception can be observed using modern imaging techniques and a physiological and behavioral response to nociception can be demonstrated. However, there is currently no objective measure of suffering.

(A Galapagos shark hooked by a fishing boat)

Evidence of pain

The ability to perceive pain in animals cannot be determined directly. However, it can be derived from physiological and behavioral responses. Some signs that may indicate the presence of pain sensation are as follows:

• The animal has a suitable nervous system and sensory receptors
• Physiological changes due to harmful stimuli
• The animal exhibits protective motor responses, e.g. reduced use of affected body parts such as limping, rubbing, holding, or autotomy
• The animal has opioid receptors and shows reduced responses to harmful stimuli after the administration of painkillers or local anesthetics
• The animal shows a trade-off between avoidance of stimuli and other needs
• Avoidance due to learning ( instrumental and operant conditioning )
• High level of cognitive ability ( cognition ) and sensation