Cage Material and Food Hopper as Determinants in Rat Preference Tests
Polycarbonate and stainless steel are commonly used cage materials for laboratory rodents. The aim of this study was to assess within-cage preference of rats for cage material, when the effect of illumination was eliminated. Altogether 64 male rats were used in two different facilities. The cages were made of either stainless steel with a polycarbonate false inner half with or without a false food hopper (Kuopio) or transparent or non-transparent polycarbonate with a steel false inner half (Oulu). A video camera with time lapse recording of one second per min was used and the positions of the rats were recorded. Once each week recording started at 16.00 and ended at 01.30, and each cage was recorded when the rats were aged four, five, six, seven and eight weeks. The results were processed separately for each facility and for day and night. Statistical analysis was carried out with repeated measures ANOVA. In cages with a stainless steel body and a polycarbonate false half, the rats chose always the cage half with the food hopper, irrespective of the cage material. Thus, the food hopper is more important to rats than the material of the cage; but when the rats were allowed to choose between those two materials, both with a hopper, they favoured steel. In cages with a polycarbonate body and a steel false inner half, the combination of food hopper with low illumination was favoured during light time. In conclusion, this study shows that rats, when given a choice, prefer low illumination and cage material may be of less importance.