Analysis of Individually Ventilated Cage (IVC) Microenvironments During 21-d Cage Change Frequency for Mice Using Two Different Bedding Types
The Guide for the Care and Use of Laboratory Animals provides recommendations on sanitation frequencies for rodent caging equipment; however, it allows for performance standards to be used when extending this frequency for individually ventilated cage (IVC) caging. Our institution wanted to reexamine our current standards of care for mouse IVC caging, which includes a 14-d cage bottom and bedding change as well as the use of corncob bedding. This was driven by desire to reduce the stress to mice associated with cage change, and by recent literature showing a potential improved absorbency and multiple health and welfare benefits of paper pulp cellulose bedding products. Therefore, this study sought to compare the impact of different rodent bedding types (paper pulp cellulose and corncob) on mouse IVC microenvironmental parameters over a 14-d compared with a 21-d cage change frequency. Ammonia levels, temperature, humidity, urine latrine size, and the overall animal condition were assessed throughout the 21-d period. Our data indicate that IVC cage bottom and bedding change can be extended to 21 d for either paper pulp cellulose or corncob bedding based on ammonia levels, temperature, humidity, and the animal’s overall condition. However, based on early cage change criteria, more frequent cage changes may be warranted before 21 d in cages with corncob, as there was a significantly increased urine latrine size in cages with corncob bedding compared with paper pulp cellulose bedding.
Ammonia was measured in each cage using an ammonia gas detection tube (while the cage remained on the ventilated rack) by the use of a predrilled hole in the front of the cage. (A) The hole was positioned on the midline approximately 6 cm from the cage bottom as shown by the yellow outline. (B) During measurements, reagent tubes were inserted approximately 6 cm into the cage while attached to a sampling pump.
Ammonia levels (ppm) were evaluated in both PPC and CC bedding types. Weekly measurements of ammonia levels in PPC-bedded cages were compared with ammonia levels in CC-bedded cages. There were no significant differences in ammonia levels at any time point between the PPC- and CC-bedded cages. There was no significant difference in ammonia levels from day 14 to 21 in either bedding type when compared with themselves. Significance was determined for P < 0.05. Data are shown as mean ± SEM.
Urine latrine size (cm2) was evaluated in both PPC and CC bedding types. Weekly measurements of urine latrine size in PPC-bedded cages were compared with urine latrine size in CC-bedded cages. There was a significant increase in urine latrine size in CC-bedded cages at days 7, 14, and 21 compared with PPC-bedded cages. Urine latrine size was evaluated for the different bedding types independent from each other at day 14 compared with day 21. There was no significant difference in urine latrine size from day 14 to 21 in PPC- or CC-bedded cages. *, P ≤ 0.05; †, P ≤ 0.01. Data are shown as mean ± SEM.
Assessment of cages that reached the University of Chicago’s early cage change criteria based on urine latrine size greater than 19.4 cm2 (3 in.2). CC-bedded cages had a significantly higher number of cages needing the early cage changed compared with PPC-bedded cages on days 7, 14, and 21. *, P ≤ 0.05; †, P ≤ 0.01. Data are shown as mean ± SEM.
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