Overview
While most people know what pain is, few understand it, especially pain in animals.
There are many misconceptions about pain and animals. For example, because a pet is not moaning or crying out does not mean it is free of pain. Most animals (unlike humans) are quite long-suffering and less vocal about their pain. From a survival point of view, it is more to their advantage to suffer quietly so as not to draw the attention of predators to themselves. Similarly, because a cat is purring does not mean that it is content. On the contrary, cats may purr if upset, afraid or in pain. It is also wrong to assume that pets do not feel pain the same way we do. Based on physiological and neurological studies, it has been shown that animals feel pain in very much the same way that we do.
Identifying Pain
For these and other reasons, the veterinarian and the pet owner must look carefully to determine whether or not an animal is in pain. There are certain indications or signs that one can look for. For example, certain behavioral responses may suggest pain. Vocalization (crying out, whimpering, growling, etc.) can be an indication of existing pain. Commonly a pet will retreat from the family or try to hide and be left alone. The pet may appear uncomfortable, which manifests itself in the form of pacing, restlessness, and repeatedly assuming different positions (e.g. arched back, forelegs held out from chest wall, in a prayer position). Often, an animal in pain will pant excessively. Some may growl or snap if handled, while others may simply grunt or try to get away. There may be a reluctance to move. Frequently, there may be a decrease or lack of appetite, listlessness or lethargy, and decreased personal hygiene (especially in cats).
Body language can be very important. For example, if there is localized pain, the animal may lick or bite at the area that is painful. If it has a broken leg or paw, it will try to hide the leg by tucking it underneath itself. These animals will also limp or not bear any weight on the affected limb. If there is abdominal pain, some dogs will stretch out and assume a praying position (called a "posture of relief").
There are also clinical signs that veterinarians look for that tell them that an animal is in pain. Dilated pupils, increased heart and respiratory rate and increased blood pressure indicate the presence of pain. Sometimes signs are not well correlated with pain since like people, cats and dogs have different thresholds for pain tolerance.