One possibility to improve laboratory conditions for animals is to conduct the experiments in a home-cages manner. For the experiments presented here, the RFID (radio frequency identification)- based IntelliCage (IC) served as an automated and home-cage-based test system. Chapter 2 describes behavioral methods that are available to assess the burden on laboratory animals in animal studies. It describes the importance of examining animal behavior in order to conclude about burden, for example, by assessing activity. By using preference tests, the perspective of the animals can be included, since the animals are (indirectly) asked what they want or do not want. The Consumer Demand test then offers the possibility to determine the strength of the preference or aversion. Through the Cognitive Bias test, it is also possible to measure the emotional state of the animals. In chapter 3, the IC was used in a long-term study to cognitively stimulate mice in the IC repeatedly, while at the same time another subset of mice was never cognitively stimulated. However, the study showed treatment effects only in the early life phase of the mice. Young mice that were cognitively stimulated showed higher activity, lower growth and a lower resting metabolic rate. They were also less attractive to female mice. However, these results were not evident at later life stages. Furthermore, no effect of cognitive stimulation on dominance or longevity could be detected. In chapter 4, an extended IC based set-up (IC and home-cage connected by a gate) was used to investigate the strength of preference/aversion for different liquids in a Consumer Demand test. For this, the mice had to make more nosepokes daily to gain access to different liquids. The data show that the number of nosepokes was dependent on the liquids offered. The mice made many nosepokes to avoid drinking a bitter-tasting liquid, while they made significantly fewer nosepokes to gain access to sweet-tasting liquids. In chapter 5, the extended IC based setup was used to develop a home-cage based Cognitive Bias test. In this study, the focus was on three developmental steps leading to a functional testing protocol. We showed successful conditioning, as well as measurement of cognitive bias in female mice. In chapter 6, the main developmental challenges and advantages of using the home-cage based system but also limitations are summarized. For instance, the method of RFID transponder implantation had to be improved, or various technical problems had to be solved. Chapter 6 also describes the advantages of using home-cage based systems. We were able to successfully record the behavior of mice over several months. We obtained individual data, the mice were tested in their familiar environment and during their natural active phase. The influence of the experimenter was reduced to a minimum, as well as the influence of the mice on each other, when only one mouse could stay in the IC at a time and thus solved the tasks undisturbed by group members. In conclusion, performing home-cage based experiments offered the possibility to refine the laboratory conditions for laboratory animals. This will again help to obtain valid data, which will be beneficial for humans.
