Whether you're breeding 100 mice or 10,000, setting up your breeding facility correctly at the beginning can prevent a lot of problems and heartbreak down the road.

If you can think of a problem, it has happened to someone before, in many cases with disastrous consequences. No one wants to come home from vacation to find that your rodents are floating down the hallway and you've made the 6 o'clock news.

First, you need to determine your needs, as this will set the size of the breeder colony you need and the space and caging required. We've already determined that we will need to produce at least 8,000 mice in a 12-month period. A mouse's reproductive cycle is roughly 20 days, and then they are immediately ready to breed again. We will need at least 1000 litters in 12 months. Rounding up to 30 days between litters, we need to produce 84 litters per month to reach that number, or in plain numerical terms 84 producing females.

The number of males required will be set by the total number of mice each cage will support. For our cages we'll be using one male for every three females in each cage, so we will need at least 28 males. Larger tubs, such as bus tubs, usually support larger groupings of between six and eight mice. In a perfect world we would need 112 mice total to keep our colony fed for a year, along with caging, food and water, and other basics.

However...

Because mice are horrible at math, and nature is unpredictable...

We will base our first mouse colony on having 200 mice, in 50 cages. That will provide for a backup in case of slow production, cycling of new and retired breeders, and insurance against accidental losses. Hopefully it will provide a small backstock of over-production and allow for rapid expansion when the time comes.

Housing 200 mice is something you don't want to do in your house, or worse, your apartment. The risks of cross contamination are simply too great. In a best case scenario all animals, mice included, should be sited in a separate outbuilding, ideally one that can be decontaminated if not sterilized. While people have been using wooden buildings to breed mice for years, if you're starting from scratch there are other better options to consider.

Many breeders use steel sheds, others use custom metal buildings. We chose a 20-foot steel CONEX shipping container. With only a wooden floor that can be removed and replaced as needed, it's almost the perfect solution. Almost.