The 3-D cage may have limited the space for the rats to gather as a group as well as perform certain behaviors such as grooming. The space available outside the L-shaped perimeter allowed the rats to continue to eat, groom, and interact, if they chose to leave the center where the rest of the group slept. The true preference test lied in the comparison of the HP vs STD cage. The rats continued to choose the HP at a significantly higher rate. However, the reduction in occupancy of the HP from 79.6 percent to 66 percent suggests that the increase in density from 6 to 12 rats is reaching the maximum limits of the HP cage.
Further study is warranted.
The rats chose social interaction and security over extra floor space, thereby defining what their needs really are when it comes to space. In the midst of the revision of the PHS Guide to the Care and Use of Laboratory Animals , it is imperative that researchers attempt to quantify what animals inherently need. It should not be merely a guess at numbers. However, we should continue to strive to improve their way of living, as they have continuously done for us. This research was supported by the National Aeronautics and Space Administration.