Pain is an unpleasant sensory experience associated with physical damage or emotional experience. Although it is essentially a sensation, pain has a strong cognitive and emotional component which can be described in terms of suffering. Animals feel and anticipate pain through similar mechanisms to those of man, therefore it is an obligation of Veterinarians to promote an effective analgesic strategy.
In order to provide adequate pain control is necessary to recognize and assess pain in animals. However this is challenging task, since these individuals are not able to communicate verbally. The recognition of pain in animals is based mainly on observation of behavioral changes, which should be specific for each species. Physiological parameters, such as increased heart rate and blood pressure, may also be incorporated into the process of pain evaluation, but should not be used alone, as they may be modified by other factors unrelated to pain.
After overcoming the challenge of recognition, the next step is to quantify the painful experience, to determine the need and effectiveness of analgesic intervention. For a long time quantification of pain in veterinary medicine was restricted to the use of unidimensional scales, such as the simple descriptive, numerical rating and visual analogue scales, adapted from human medicine to be employed by an observer. However, the lack of an objective criterion to guide pain assessment makes these scales subjective and dependent on the observer's experience.
In order to limit the subjectivity and increase accuracy in the recognition and measurement of pain in animals, studies have directed attention to the development and validation of assessment tools specific for each species focused on detailed description of behavioral changes. When validity and reliability of these instruments are established, they are the most accurate and reliable information to assess and quantify pain in the species concerned.