How to Recognize Pain in Animals

This website is intended to provide general guidance on recognizing pain in animals based on findings in the National Research Council report, Recognition and Alleviation of Pain in Laboratory Animals (2009). For in-depth discussion and for information on preventing and alleviating animal pain, see the full report.

All vertebrates should be considered capable of experiencing the aversive state of pain. The alleviation and prevention of animal pain is both an ethical and moral imperative. In the case of lab animals, minimizing animal pain is also scientifically and practically beneficial. What has been learned through research about pain in laboratory animals can also be applied to pets, farm animals, and other animals.

General Overview: Behavioral Signs of Persistent Pain

Recent scientific research has considerably advanced our understanding of animal pain; however, there are still few scientifically validated pain assessment techniques. Therefore, in most circumstances, pain is assessed based on the appearance of an animal and its overall behavior. Current best practice is to combine a structured clinical examination with a good knowledge of the normal appearance and behavior of the animals involved.

Here are some signs to look for:

Sign Explanation
Guarding The animal alters its posture to avoid moving or causing contact to a body part, or to avoid the handling of that body area.
Abnormal appearance Different species show different changes in their external appearance, but obvious lack of grooming, changed posture, and a changed profile of the body can all be observed. In species capable of some degree of facial expression, the normal expression may be altered.
Altered behavior Behavior may be depressed; animals may remain immobile, or reluctant to stand or move even when disturbed. They may also exhibit restlessness (e.g., lying down and getting up, shifting weight, circling, or pacing) or disturbed sleeping patterns. Large animal species may grunt, grind their teeth, flag their tail, stomp, or curl their lips (especially sheep and goats). Primates in pain often roll their eyes. Animals in pain may also show altered social interactions with others in their group.
Vocalization An animal may vocalize when approached or handled or when a specific body area is touched or palpated. It may also vocalize when moving to avoid being handled.
Mutilation Animals may lick, bite, scratch, shake, or rub a painful area.
Sweating In species that sweat (horses), excessive sweating is often associated with some types of pain (e.g., colic).
Lack of Appetite Animals in pain frequently stop eating and drinking, or markedly reduce their intake, resulting in rapid weight loss.