Exposure in the Shoebox: Comparison of Physical Environment of IVCs and Open Rat Cages

Abstract

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.