How low can you go? Using bottle volume as an alternative to time-scheduled water bottle replacements for mice. Alyssa L. Valentyn, Venus Estrada, Naina Silva, Misty Williams-Fritze, Laurette Burgess.
The use of sterile disposable cage components has led to an increased need for performance-based standards. The Guide specifies that sipper tubes require weekly sanitization. However, the gravity-drip design of the water bottles our institution uses should minimize contamination, suggesting water quality and cleanliness may be maintained for longer durations. Weekly changes for disposable bottles yield abundant plastic and water waste: bottles are typically greater than half full at seven days, even in densely populated cages. Caps must be removed and bottles emptied in order to recycle—a labor-intensive and ergonomically challenging process. A volumebased schedule is a visual alternative to weekly changes, reducing the number of bottles processed and facilitating operations by allowing spot changes without the need to track bottles. We hypothesized that extending bottle duration from weekly to volume-based would not adversely affect mouse health or water quality. 100mL was chosen as the lower limit, as this represents an approximate 4-day supply of water in densely populated cages. We collected baseline (7-day) data from 15 cages of C57BL/6NCrl mice at various housing densities (ranging from 1-5 mice per cage) for changes in animal weight (measured weekly) and average water consumption (measured every 2-5 days). At bottle replacement, we measured packed cell volume (PCV) as a marker of clinical dehydration and assessed water quality by visual inspection, plating for E. coli and coliform bacteria, and total microbial count. We repeated these assessments, leaving bottles on the cage to 100mL (13-47 days, depending on cage density). No difference was observed in animal body weight, body condition score, average water consumption, or PCV, regardless of cage density or the amount of time the bottle was deployed. Average water consumption was maintained at an average rate of 3.9 ± 3.5mL/ mouse/day for both seven-day and volume-based changes. Microbial analysis showed no bacterial growth in any bottle, and visual inspection showed no turbidity or cloudiness. We conclude that, at our institution, pre-filled disposable, acidified water bottles can be extended beyond seven days using a volume-based replacement at 100mL, with no adverse effect on animal welfare.