The challenge my lab faced:
At the highest point, our lab had over 400 cages of mice. There were mice that were over two years old, with absolutely no use to our studies. We were breeding conditional knockout mice, as well as six other strains of mice, and the sheer volume was overwhelming. Additionally, we initiated experiments at specific ages (6 or 12 weeks), so we needed to know what mice we had, at what age, and what their genotypes were.
The small thing that we changed:
We began by culling the number of mice we had. Mice that were not going to be used were eliminated, while we streamlined the remaining mice from the seven strains. We kept a spreadsheet on our server (accessible by everyone), with a column that autoupdated the mices ages (denoted in weeks). Once an experiment began using the animal, they were taken off the available mice list and moved to an experimental list. Once the mouse was sacrificed, they were eliminated from the system.
The impact this had on the lab:
We were able to pare our colonies down to less than 100 mice and were able to manage breeding, experiment initiation, and mouse availability all in one easily accessible spreadsheet.