The Guide does not specify the acceptable rationales for and purposes of research involving laboratory or field (natural state) animals. It says that there must be an acceptable rationale and acceptable purpose. There are restrictions, of course, and these may impinge upon the researcher, forcing him or her to modify their animal use ideas.
The silence of The Guide on rationale and purpose lays the two essential questions in the hands of scientists and laypersons serving on the IACUC which is composed of scientists, a laboratory animal veterinarian, a community member, an ethicist, and a University administrator. Experimental design is evaluated to whether the life of that animal, given the cost to it, can provide valuable information toward the progression of science.