I breed especially for my cats. I feed twice a day and each feeding session takes 40-50 adult mice (~30g each), so breeding my own mice is more cost effective.
I pre-kill and then freeze the mice for about a week. If you're going to feed to cats, it's really in your (and your cat's) best interest to freeze the mice first, so that you make sure to kill any Toxoplasmosis cysts that may be present in the mouse. Freezing the mice to 10F/-12C or colder for at least 3 days kills the tissue cysts and breaks the cycle, which helps keep you and your cat safe and sound. It's especially important for people with compromised immune systems or who are/may become pregnant.
My cats don't care if the mice are frozen first, as long as I warm them up before I feed them. I usually take them out of the freezer the day before and thaw them overnight in the fridge. Then, I soak them in ~100F water for about 15 minutes immediately before feeding.
I have a second fridge
and a chest freezer just for pet food