Pain is an unpleasant sensory and/or emotional experience associated with actual or potential physical damage. Pain has sensory, cognitive, and emotional components, related to previous experiences, and is usually expressed by behavioral changes. Animals feel pain through the same mechanisms as humans, hence it is our moral and ethical obligation to alleviate pain.

To treat pain, it is necessary to recognize it. Animals do not express themselves verbally like humans, so behavior is the main and easiest way to identify pain in animals. Physiological indicators can also be incorporated to assess pain, such as heart rate and blood pressure. Every species demonstrates specific behavior, so pain scales must be unique to each species.

After recognition, pain should be quantified to determine the need for and type of analgesic treatment. In the past, unidimensional scales adapted from humans were used, such as simple descriptive, numerical, and visual analogue scales. However, these are subjective, depend on the observer’s experience, and are not readily reproducible.

Validated scales, unique to each species, based on behavior, are the most appropriate to assess and quantify pain in animals as they ensure greater accuracy of validity and reliability.