Assessing Accumulation of Organic Material on Rodent Cage Accessories

Abstract

According to the 8th edition of the Guide for the Care and Use of Laboratory Animals (the Guide), rodent cage accessories, such as filter tops, should be sanitized at least once every 2 wk. We performed a study to test the hypothesis that organic contamination (measured by ATP content, expressed as relative light units (RLU)) of cage accessories (wire bar inserts and filter top lids) does not differ at 2 wk (14 d) as compared with 30, 60, and 90-d time points after cage change even when in constant use. An additional time point for filter top lids of 180 d after cage change was also evaluated. Eight groups were studied: the wire bar inserts and filter top lids used for mice and rats, in both static and individually ventilated cages (IVC). When analyzing data from both mouse and rat static and IVC caging, we found that the mean RLU values for mouse IVC and rat static and IVC cage components were below 100,000 RLU at the 14-d time point. The mean value for the mouse static group was slightly above 100,000 RLU at this time point. Based on this observation, we considered 100,000 RLU to be an appropriate actionable level. We concluded that changing wire bar inserts at least every 14 d, as recommended in the Guide for sanitizing these components in mouse and rat static cages, may be considered acceptable. This interval could be extended for mouse and rat IVC cages up to 90 d while remaining below this limit. Filter top lids for mouse static cages should be changed at least every 30 d, but static rat and IVC mouse/rat filter top lids could be changed up to every 180 d, while still staying below this actionable level of contamination.

Figure 1.

Graphs depict the number of relative light units (RLU) in the 8 groups; (A) mouse static cage wire bar lids, (B) mouse IVC cage wire bar lids, (C) rat static cage wire bar lids, (D) rat IVC cage wire bar lids, (E) mouse static cage filter top lids, (F) mouse IVC cage filter top lids, (G) rat static cage filter top lids, (H) rat IVC cage filter top lids. Significant difference(s) (P < 0.05) between 14 d and other time points are marked with an asterisk *. Data is represented as the mean at each time point with standard error of the mean (SEM).

Figure 2.

Number of relative light units (RLU); mouse wire bar lids (static and IVC cages). Data is represented as the mean at each time point. The red line is the actionable level which is designated at 100,000 RLU.

Figure 3.

Number of relative light units (RLU); rat wire bar lids (static and IVC cages). Data is represented as the mean at each time point. The red line is the actionable level which is designated at 100,000 RLU.

Figure 4.

Number of relative light units (RLU); mouse and rat filter top lids (static and IVC cages). Data is represented as the mean at each time point. The red line is the actionable level which is designated at 100,000 RLU.