How To Keep And Breed Feeder Mice
Mice are small and easy to keep and breed. They are the ideal feeder for many animals. Female mice are very social and do well in groups. Males are very territorial and will fight. I have found I can keep a ratio of 2 males to 12 females without fighting. I keep my large group in a 30 gallon tank. Male mice have very strong scented urine.
Mice are escape artists and can fit through any opening they can get their heads out of. Wire cages are not recommended for use with mice. A 10 gallon tank with a mesh lid can house a buck and 2 does. Sweater box bins also work well. Make sure to cut out sections and glue in wire mesh for ventilation. Keeping them at room temperature is ideal.
A general set up is a hide house/nesting box. Any cardboard box would work or the plastic houses work as well. A water bottle can be hung up inside a tank with a piece of wire. Bedding can be paper based. Yesterdays news paper is good and cat litter works well. Aspen shavings (not pine or cedar), shredded paper (news paper, paper towels, computer paper) and hay or straw also work well.
Optional: Wheels (solid or mesh are ideal), ropes hung from the lid to climb on, toilet or paper towel rolls and toys for exercise.
Mice are omnivores and will eat pretty much everything you give them. Lab blocks are recommended. Seed mixes also work great. Hamster food is good. A home made mix including wild birdseeds, rabbit pellets, horse feed, dried bread, etc. can also be used. Adding protein like dog food, dog milk bones, scrambled eggs and mealworms will help prevent baby cannibalism.
The easiest time to sex mice would be 9-12 days old when the belly fur grows in. Only female mice have nipples. I sex my babies at birth. I like to keep my litters female heavy. Newborns have very slight differences. (see picture) Males have a bigger "bump" and the spacing is much farther apart than the females.
Male mice are able to breed around the 5 week mark. Females take a couple weeks longer. I keep my groups together as a colony so I don't have to do introductions. Mice go into heat every 3 days, so in no time your females will be pregnant. Gestation is 18-20 days. You will notice your females look like they swallowed a golf ball. Within 24 hours after delivering a female can be bred again. Litters sizes vary, usually 1-12 though 25 has occured but it is not very common.
I handle my litters early on. The best thing to do is to remove the adults into a separate tub and then check on the newborns. Remove any dead babies and if you need this size, cull some. It's best to not cull an entire litter at once. Culling 2-3 every few days is better, to prevent mastitis, which is swollen milk ducts.
There are a few traits that people who breed feeders should be aware of. There are 2 lethal genes you should have knowledge of. When the animal gets a double (homogeneous) of a lethal gene, the babies are born dead or deformed.
Here are examples of the 2 lethal genes.
Variegated (aka dominate spot). The spots have jagged edges and they often have more color than they do white.
Lethal Yellow (aka Red)
In Europe they have a lethal yellow, also a dominate trait. This gene is in America but probably has not made it to petshops or feeder bins. They are a very dark yellow to red color. This one is not genetically a Red, but she is a close match.
Brindle mice (American brindles, visable yellow agoutis) another dominate trait, are not a lethal combo but they are prone to obesity. Often, once the females get obese, they stop producing babies. I personally love the colors of brindles, so I keep them. Once they get chunky we keep them as pets.
These 2 ladies are obese brindles.
Author: Susan Wyldrose
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Care Sheet Images - © Susan Wyldrose