OPERANT STUDIES TO DETERMINE THE STRENGTH OF PREFERENCE IN LABORATORYRATS FOR NEST-BOXES AND NESTING MATERIALS

Previous work has shown that laboratory rats preferred to use nest-box es and nesting materials rather than empty parts of the cage. In prefe rence tests, they chose opaque or semiopaque nest-boxes and long strip s of soft paper nesting material. Choice tests to demonstrate a prefer ence between nest-boxes and nesting material were not possible because nesting materials were carried into the nest-boxes. Furthermore, pref erence tests did not show how important these items were to the animal s. Accordingly, operant tests were conducted, in which the rats had to lift a weighted door in order to gain access to an empty cage, or one containing a nest-box, nesting material or both items. By progressive ly increasing the weight of the door in subsequent trials, it was show n that the rats would carry out more work to reach a nest-box, with or without nesting material, than to reach an empty cage.