Regulations require that researchers refine experiments to minimize pain and distress. This is accomplished by requiring researchers to classify all animal usage in terms of amount of pain and distress and, for animals that fall into a particular classification, to justify subjecting them to pain and distress. The first step is to understand the meaning of pain and distress so that animal use can be classified. Associated distress may be relieved with tranquilizers. Acute distress can be relieved with tranquilizers.
More sustained distress requires environmental change and behavioral conditioning.
The second step is to use the understanding of what constitutes pain and distress to classify experimental procedures. The USDA requires that all animal usage be classified according to one of four types. It is important that researchers understand this classification, because procedures that fall under classification E requires special justification. Animals upon which teaching, research, experiments, or tests were conducted involving no pain, distress, or use of pain-relieving drugs. Procedures that are performed in the normal practice of veterinary medicine fall under this classifiction.