Durability and Hygiene of Aspen Tubes Used for Providing Environmental Complexity for Laboratory Rats
In Europe the provision of environmental complexity for laboratory animals is mandatory unless there is some welfare-related or scientific reason to prevent their inclusion. Any chemical compound present in the added item to the cage represents a potential confounding factor in the study. The best remedy to this problem is to use a material, such as the wooden bedding material which is already present in the cage. The durability of wooden items means they can be used several times, but they are considered difficult to sanitise. Furthermore, items that are made of several parts may be more easily destroyed than those made of a single unit. This study was designed to explore the durability and possible practical problems associated with sanitation and hygiene of a commercially available aspen tube intended for routine use with rats. The wooden items used were rectangular tubes (20 x 11 x 11 cm) made of dried aspen board with the walls being held together with aspen pins. Before the first use, all of the aspen tubes were autoclaved. At each cage change, the tubes were rinsed either under a pressure washer without detergent or rinsed combined with autoclaving. The tubes were observed for durability and sampled for microbes after use and after sanitation. All of the tubes were discarded before the 14th use. Washing as the sole sanitation method decreased total bacterial burden and coliforms during the first three cycles as compared counts prior to wash. With respect to fungi there were no differences between the sanitation groups. In conclusion, when aspen tubes are cleaned with plain water and pressure, they can be effectively cleaned for up to four cycles. When autoclave treatment is added to the wash cycle, it is the macroscopic damage, which determines the usable life of the item. It appears that aspen blocks can be used in rat cages more than once without any danger of elevating the microbiological burden.