2008 - Volume 35 - Issue 2

69-77
Cage Material and Food Hopper as Determinants in Rat Preference Tests
by H-M.Voipio, A-M. Määttä, H. Honkanen, R. Haapakoski, M. Heikkilä, K. Mauranen,
S. Mering & T. Nevalainen

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.

81-90
Work for Food – A Solution to Restricting Food Intake in Group Housed Rats?
by Niina Kemppinen, Anna Meller, Kari Mauranen, Tarja Kohila & Timo Nevalainen

Rodents spend a great proportion of their time searching for food. The foraging drive in rats is so strong that the animals readily work for food even when food is freely available. Commonly used ad libitum feeding is associated with a reduced life span, increased incidence of tumours and risk of liver and kidney diseases. It is also considered to be the most poorly controlled variable in rodent bioassays. The aim of this study was to assess whether rats will gnaw wood in order to obtain food hidden in wooden walls, whether this activity has a beneficial effect on controlling weight gain, and whether a typical diurnal activity rhythm is maintained. A total of 18 BN/RijHsd and 18 F344/NHsd male rats were housed in either open or individually ventilated cages (IVC), three rats in each cage. 10 of 36 were fitted with a telemetric transponder. Four groups were used: two groups (diet board and plain board) with a maze made of two crossed aspen boards, the third having a rectangular aspen tube. One maze was of plainboard, but the other included drilled holes snugly loaded with food pellets, the “diet board”, such that the rats had to gnaw wood to reach the food. The other two groups – and the controls – were fed ad libitum. The study used a crossover design and the added item was changed every two weeks. Rats, added items, and amount of food left at the end of the two week period were weighed. The statistical assessment showed that in terms of weight gain there was a significant interaction both in IVC- (p = 0.005) and in open cages (p < 0.001) between the strains and the group. In the F344 rats the diet board was more effective in controlling weight, but when combining the strains, all comparisons with diet board were significant (p < 0.05). Use of strain and added item as main effects, and age as covariate, showed that in the IVC-system there was a significant (p < 0.001) interaction between the strain and the group, this effect being rather clear in the F344 rats in terms of amount of food disappearing. In the open cage system, both strain and group were significant (p < 0.001) factors; all three comparisons with diet board were significant (p < 0.001) in the amount of food disappearing. In conclusion, the work-for-food approach appears to be a promising way of avoiding obesity without causing untoward effects on diurnal activity in rats. Hence, the approach may have considerable refinement and reduction potential.

97-103
Exposure in the Shoebox: Comparison of Physical Environment of IVCs and Open Rat Cages
by Niina Kemppinen, Anna Meller, Erkki Björk, Tarja Kohila & Timo Nevalainen

New caging and innovative items for more structured environment within the cage have been introduced. Many of these innovations cannot be seen as 'pure' or individual procedures, but rather they represent a mixed exposure with a multitude of operant factors, some possibly having an impact on animals and research. One kind of new caging system is the individually ventilated cage (IVC), where each cage receives its own non-contaminated airflow, primarily designed for health status maintenance and occupational safety. Even though those cages may be the same as those used in open cage systems, the physical environment inside the cage may not identical. Comparison between cage types is difficult without characterization of the physical environment, because the change may involve alterations in several parameters in the environment. The aim of this study is to characterize and compare common physical parameters in the ordinary situation, where IVC-racks are kept in the same room with open cages. The cage type used was a polysulfone solid bottom cage. The parameters measured in this study were: illumination, temperature, relative humidity (RH) and acoustic level in both IVCs and open top cages. No animals were in the cages during light intensity, but there was bedding in the cage during acoustic measurements and both bedding as well as a half-full food hopper during the illumination measurements. The temperature and (RH) measurements were carried out with three male rats in each cage. There were differences between IVCs and open top cages in all measured parameters. The light intensity was lower in IVCs, most likely due to more compact cage placement in the rack and the additional plastic cover lid of the cage. Both maximum and minimum temperatures were 1-4 oC higher in IVCs; which suggests that their ventilation is incapable of taking away heat, produced inside the cage. Similarly, the relative humidity was higher in the IVCs. The sound level adjusted to rat's hearing with R-weighting was higher in IVCs when compared to open cages. Furthermore, the sound level was highest in the corners next to the ventilation valves. In conclusion, there may be differences between open cages with IVCs involving several physical parameters of cage environment and this may confound comparisons between results obtained in these cage systems.

107-115
Durability and Hygiene of Aspen Tubes Used for Providing Environmental Complexity for Laboratory Rats
by Hanna-Marja Voipio, Tuula Korhonen, Tarja Koistinen, Henry Kuronen, Satu Mering & Timo Nevalainen

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.

119-123
Using Airshowers to Decrease Laboratory Animal Allergy
by Thomas C. Krohn, Klaus Vognbjerg & Axel Kornerup Hansen

Airshowers may be an effective way of removing allergens from the clothing and uncovered skin and hair of personnel, but the optimal shower time and air speed for this use have not been elucidated. The aim of this study was to test the effect of differences in clothing type, shower time, and air speed on the efficiency of allergen removal by airshowering. In general we found that as air flow rate or shower time increased, so did allergen reduction. When tested in a real-life situation, the airshower removed more than 98% of the allergens from the shoulder area of personnel and more than 87% of the allergens from the thigh area. In addition, the allergens remaining after airshowering were not spread when protective clothing was removed. Factors such as clothing type, air speeds, and showering time need to be considered when establishing standard operational procedures for the use of airshowers.

127-134
Effects of Litter Origin and Weight on Behaviour of Outbred NIH/S Mice in Plus-maze and Staircase Tests
by Kai Õkva, Aavo Lang, Timo Nevalainen, Kari Mauranen, Marika Väli & Paavo Pokk

The objective of this study was to investigate the effects of litter and weight on the behavior of mice. Male outbred NIH/S mice from 8 litters were randomly distributed among 6 cages and subjected to the plus-maze and staircase tests. The litter from which the animals had originated had a significant effect on the behavior of mice in the plus-maze test; furthermore addition of the covariates final weight and weight gain had no effect on significance or explanatory value. It is proposed that litter origin might influence the adaptation processes, the development of social status and consequently, the behavior of mice. Differences attributable to litter were not observed in the staircase test, but when both weight parameters were added as covariates this proved to be significant. Though the source of these litter-related differences remains to be clarified, these differences do have a significant effect on the behavior of mice. Therefore they need to be considered since knowledge of the litter where the outbred mice originated can partly explain differences in the behavior of the animals. The comparison of models showed that incorporation of the natural features of the animals (as derived from their biological origin) into a calculation can help rationalise the results; and provide ample opportunities for discussion and understanding of this complex issue.