Institut für Physiologie, Veterinär Medizinischen Universität, Wien, Austria
Nesting material, tubes and/or nest boxes appear to be suitable enrichment items for laboratory mice. Choice tests can help us to assess the value of these items from the animals' point of view, and to find out which materials and measures they prefer. The test system is similar to the one described by Blom et al. (1992, 1993). It consists of four Macrolon Type III cages, which are connected to a central circular corridor by perspex tubes. In order to facilitate observation, the lids of the cages are substituted by perspex frames. The test cages are equally equipped with sawdust bedding, a water bottle and pellets in a dish.
For the first experiment, the test cages were structured as follows: (A) paper tissue, nest box, cardboard roll; (B) paper tissue, two cardboard rolls; (C) paper tissue, nest box; (D) no additional structures. 24 female and 8 male outbred mice (Him:OF1) were tested after weaning in groups of four. Eight female outbred mice (Him:OF1) were tested at the age of 10 to 12 weeks two by twos. All animals had been reared in conventional Macrolon Type II or Type III cages with sawdust bedding only. Artificial light is from 07.00 to 17.00, light intensity about 100 lux on the floor of the test system. The animals' behaviour is recorded by video (infrared light during the dark period) from 16.30 to 21.30 and from 06.30 to 11.30. During the first 48 hours of the experiment, the animals' behaviour is recorded continuously and by scan sampling. The preference test is started after 48 hours of exploration and habituation to the test system. For the preference test the mice are observed by scan sampling from 17.00 to 21.00 and from 07.00 to 11.00. Their location in the test system, their discernible activities (locomotion, being active without locomotion, feeding, drinking, resting, being hidden in one of the test structures) as well as vicinity of other mice and contact with enrichment structures are recorded in 20 second intervals. As soon as the mice have built their nest in one of the test cages and rested there during two consecutive days, this "preferred" cage is emptied, and the choice test repeated with three test cages only. Two to four days later, when the mice have again made their choice, the second preferred cage is emptied, and the choice test repeated with two test cages.
Scan sampling proved to be a suitable method for choice testing. As far as the light period is concerned, the majority of mice (28 from 38 animals tested so far) preferred cage A, followed by cage C and then B. One group of male juveniles (4 animals) and 2 adult females preferred cage C, followed by cage A and then B. The bare cage D was rarely visited during the light period, but frequently occupied when the animals were active in the dark.
The cinematografic method of choice testing has the advantage of group testing, and it can give some information about the animals' behaviour in the test system. Although a suitable event-recording program (The Observer 3.0 for Windows) was used, the method is still time-consuming and not easy to employ with four animals. Further methological development and an analysis of social behaviour in the test system are required.