Animal Welfare Enhancement Awards - 2005 Recipients

Mouse Preference for Cage Changing Interval: Are Soiled Cages Affecting Mouse Well-Being?
Tamara Godbey, DVM
University of British Columbia

The environments of most laboratory animals have been developed based on factors other than animal preference or a simulation of the animals' natural environment. This is especially true of the laboratory mouse, one of the most widely used species in research. With the growing use of individually ventilated cage (IVC) systems for mice, the interval for cage changing has increased based on empirical manufacturer recommendations. This increase in interval leads to a decrease in the amount of bedding used and a decrease in the number of hours needed to change cages. Rather than the standard one-week interval for other caging systems, the IVC system manufacturers have recommended from 14 to 21 day cage changing intervals. We question the appropriateness of this increase in cage changing interval and wonder how this may affect mouse welfare.

We have designed an experiment to evaluate mouse preference for cage changing interval. Using time-lapse infrared video, mouse movements and behaviors will be evaluated when given the option of movement between cages with different degrees of soiling. To further evaluate preference, the study design includes the absence of food and water in either the "cleaner" or "dirtier" cage. Based on optimal foraging theory, we would expect the mice to remain close to the food source.

We expect this new information to be valuable in the development of best management practices for laboratory mouse husbandry. We believe animal preference should be as important as economics in deciding husbandry practices.

Hypothesis and Experimental Design

Our hypothesis is that mice will not show a cage preference (i.e., increased dwelling time, presence of nest) based on the degree of cage soiling. To test this hypothesis, we will determine percent dwelling time when mice are offered cages of various degrees of soiling (i.e., 7, 14 or 21 days) in a simple two-choice preference test.

The experimental arena will consist of two standard open-topped polycarbonate shoebox cages linked by 2 ft. of wire mesh tubing. We selected mesh tubing based on preliminary studies where mice used the clear plastic tubing undesirably as a hiding place and/or latrine. Cages will contain equal amounts of wood shavings, environmental enrichment (i.e., amber colored mouse igloo) and one brown paper towel for nesting. Mice will be offered Purina Mouse Diet and tap water ad libitum.

In order to reach the desired degree of soiling in each cage, mice will be moved between two sealed-off cages in cycles of 2 or 3 days: 1 day. For example, the mice will be placed in the first cage for 2 or 3 days, then moved to the second cage for 1 day, returned to the first cage for 2 or 3 days, etc. until the desired levels of soiling has occurred. The following combinations will be tested: 7 vs. 14, 7 vs. 21 and 14 vs. 21 days of soiling. Mice will be hand moved between cages by one individual to avoid variability in handling. The arena will be turned 180 degrees daily to avoid a possible mouse preference for one side of the apparatus due to external variables such as lighting or air movement. After the predetermined soiling period, tube barriers will be removed and the mice will be allowed to move freely between the cages. Mice will be monitored 24 hours a day by infrared time-lapse video for the 7 days following the soiling period. Percent dwelling time between the 2 cages will be determined as well as daily record of nest position.

Mice will be grouped in cohorts of 2 or 4 of the same sex and age and will be naïve to the degree of soiling (i.e., raised in cages that are changed once weekly). Any available inbred or outbred strains of mice at UBC will be included in this study and randomly assigned to a treatment group. In the initial trials, we will provide equal amounts of food and water in both cages in the arena. However, if we find a significant preference for the less soiled cage, we will use optimal foraging theory to design additional experiments to further investigate the strength of this preference. In these subsequent trials, food and water will be restricted to only one of the cages during the monitoring period.