Environmental Monitoring to Support Extended Cage Change Frequency in Mouse Individually Ventilated Cages (IVCs)


Problem statement: As a facility manager, I must consider what is best for both animal welfare and the researchers/staff who work with the animals in our facility. Asking “why” is one of the important aspects of the IACUC's role. This important question is why many improvements have been made to animal welfare and husbandry practices over time.  Previously, our facility changed rodent IVCs every seven days, which was observed by animal husbandry staff to be excessive. The question arose when switching to a new bedding substrate: can we extend our cage cleanings and improve our husbandry practices? The IACUC played a pivotal role in helping our animal technicians submit a protocol and conduct the pilot study. The basis of the study was to determine if cleaning mouse cages could be extended to every 14 days, and in what ways would that be beneficial.

Description of research: The purpose of this study was to measure temperature, humidity, and ammonia levels inside mouse IVCs to support extending cage cleaning to every 14 days with compacted cellulose 1/8” bedding. Different social housing densities (one, three, six and dam with litter) were studied with C57/B6 mice of both sexes. Routine cage changes are required in order to limit ammonia levels within the mouse microenvironment, but the frequency of which can negatively affect both animal and human welfare. Cleaning less frequently can help improve negative stereotypic behaviors in rodents (Rosenbaum 2009) and limit staff exposure to allergens, ergonomic injury risk, and zoonotic diseases. Most cage change intervals have been set based on visual cues indicating a dirty cage and the odor of ammonia, which humans can detect at 0.4 ppm, far below the suggested maximum within the mouse microenvironment (Brown 1993; Rosenbaum 2009). This suggests that it may be possible to extend the time between cage changes without exposing animals to high levels of ammonia. Previous literature supports the ability to extend mouse cage changes up to and past 14 days while housed in IVCs, dependent on the type of bedding substrate used, and amount of air changes per hour (Ferrecchia 2014; Smith 2004). For this study, 50 ppm was the maximum level of ammonia allowed. The highest average ammonia level observed during the study was five ppm in the cage housing a dam and litter. It was determined the cage change frequency for all mouse cages within the facility could be extended to every 14 days and possibly even longer. The IACUC should encourage additional pilot studies performed by husbandry staff to refine best practices within their facilities. Bridging the gap between IACUC and husbandry staff at our facility allows additional studies to be conducted which can continue to refine best practices. The next step is to conduct a similar study examining current environment conditions within rat IVCs.

Additional Information: Providing staff with opportunities to advance their skills, knowledge, and interaction in their work environment can be beneficial to both the facility and animals, and in the retention of employees. Given the chance to conduct a study of their own, animal care staff found it insightful and educational to experience what is required to conduct a live animal study. Having researchers and members of the IACUC willing to mentor those unfamiliar with conducting a study and submitting a protocol is important for success.