Mice Breeding

by  Simon Watharow

Po Box 4499 Wantirna, 3152 Vic


The standard laboratory mouse is currently a source of food for many if not most species of endothermic (warm blooded) feeding for reptiles in captivity. To cater for the welfare and correct treatment of this food source, a detailed care sheet will be provided here. My aim in this article is to provide details on the various aspects of mouse husbandry and highlight important husbandry tips. Regardless of the reason you breed mice it is essential that the correct care and treatment of this delightful animal be accomplished.

The Mouse

Originally bred in the Eighteenth century from wild mice by fanciers. A prolific breeder that has been used world wide for research.

Key factors for a good food source

  • Inexpensive to buy
  • Hardy
  • Breeds readily
  • Short gestation periods
  • Large litters
  • Readily available
  • Small size means smaller cage size and makes them easier to handle

Biological Data

Adult weight

Male 20 -40g

Female 18 – 35g

Lifespan 1 – 3yrs

Gestation 19 – 21 days

Weaning 21 days

Mice are nocturnal and very sociable animals. They have relatively poor eyesight, but excellent hearing and a good sense of smell. Mice should be maintained in-groups usually formed at a young age.

Handling mice by their tail is the safest and most convenient way of moving them from box to box.


Mice have been proven to prefer smaller so-called shoebox style enclosures with a wire lid. Importantly in mice breeding are enclosures that have reduce draughts, prevent excessive light and conduct less heat.

The majority of enclosures used these days are old laboratory style cages. Made predominantly by a Melbourne based company called “Wiretainers”. However there are many enclosure types. The shoebox / rat cages are very durable, easy to clean and are stackable. Fitted with a wire lid in two forms at present flush or a raised top, which is excellent for rats. They usually have wire lids with indentations made for food and a hole/s, which accommodate water bottles. So what else can you use?


These are some possibilities, which very much depend on the quantity of animals you intend to house and breed. Remember mice are very skilled at escaping, can jump and fit through very small gaps (e. g. adult mice can squeeze through chicken wire). So a well-sealed enclosure is needed.

Aquariums: The aquarium is perhaps, the most common choice for housing mice. Its tall sides and enclosed frame offer, not only an enclosed environment, but can make it easy to clean. The down side is the weight and awkwardness of moving or cleaning. Aquariums are easily and almost inevitably damaged, chipped, cracked or broken.

Storage Bin / Habitat Tanks: Can make an excellent alternative cage for mice. Plastic storage bins used for storing clothes, tools, etc. They are clear, or frosted, tough plastic. The mice can be easily seen through the sides. They come with a plastic lid that snaps down firmly in habitat tanks. These lids in storage boxes should have a section cut out and replaced with wire or nylon mesh. This will enhance ventilation in the box.


Mice are known to clearly prefer a box with a solid floor and bedding material and an dark enclosed hide. Wire floors are not usually acceptable in the modern breeding facility. Sawdust is the most frequently used substrate in the research area but there may be other choices. Cat litter pellets or grains could well be used to control odours and prevent excessive dampness, shredded paper is also a good idea but do not use newsprint (newspapers contain ink which when wet stains the feet of rodents). Try to be environmental friendly by using discarded paper, or shredded boxes. Sawdust also comes in handy and is still cheap and readily available.

Nesting Materials should always be given regardless of breeding condition, commonly shredded tissue paper or paper is accepted.

Housing density

So how many can you have in a box? Defined for the purposes of safe, responsible and with the welfare of mice in mind. The shoebox style enclosure should have up to three females and a male for breeding and ten to twelve mice for maintenance. The standard laboratory size box can house up to twenty mice. The research has proven over the years that overcrowding is stressful, lowers reproductive success, and encourages disease and lowers immunity. In the quest for production of large numbers of mice it is requested that you try to keep welfare in mind.

In the animal house situation most mouse groups are formed when young and rarely are new animals placed in them Mice form strong social ties and will reject mice taken away and returned after a long absence. They form rigid relationships within the groups.

Male mouse breeders and lactating female mice are very intolerant of strangers.


Mice have a thermal requirement, which can range from 18 -26 degrees Celsius, with the mean around 22 degrees Celsius.


Provided best in a bottle glass or see through plastic. Stoppers should be firm rubber and pipes stainless steel. There are some commercial products that can be bought e. g. Cranberry glass bottles that can be adapted to mouse or rat bottles. Water should be changed every two to three days and bottles rotated every two-weeks and disinfected with a 2- 5% bleach solution.


Barastoc GR 2 and Clark King are the two well-known rodent pellet producers, as well Norco also provide pellets. Mice also enjoy treats or scraps e. g. carrots, apples, biscuits, rice crackers and bread. Females lactating with young will eat up to four times as much food to provide for the litter. Food pellets is usually supplied ad lib (as much as they want to eat).

Environment enrichment

To create better environments for the mouse as well as place to hide and stimulate better breeding try some of the following.

  • Many commercial pet shops have plastic see through pipes, which can stimulate activity. But you can use left over plumbing PVC pipes.
  • Paper Towel/Toilet Paper rolls.
  • Paper clips attached to wire lids.
  • Shredded paper left on wire lid.
  • Egg Cartons (cardboard only).
  • Light bulb boxes, cardboard boxes (cereal boxes etc) cut into small squares (enough to fit several mice).
  • Mailing tubes or other small disposable boxes.



Sexed when young by the ano genital (distance between anus and genital) distance. Determining the sex of mice is accomplished by comparing the distance between the anal opening and genital papilla (ano genital distance). This distance is shorter in females and greater in males.

Determining the sex of very young mice may be difficult for the beginner, and it is often helpful to compare a number of littermates.

In older mice, the males have testes while the females do not also the presence of nipples indicates a female, as male mice do not have nipples.

Breeding Methods

The mouse is an exceptional animal to breed its smaller size and relatively easy handling make it ideal for the beginner. Random breeding is what most mouse breeders for food productions do. This is where animals are selected from random sources with no genetic or desired characteristic been maintained. It is important to continue to get outside stocks to keep genetic stability. Other wise you could inbreed the stocks you have. Inbreeding can lead to decreased litter size, mutations, susceptibility to disease and mortality.

Harems are the choice for breeding mice. Commonly two females and a male in a shoebox enclosure is best. It helps to record dates of birth so as to keep track of litter sizes and frequency of breeding. Mice are best rotated after twelve to eighteen months of breeding as the litter size reduces greatly after. So plan your stock to have new breeders to take over from the older harems.

Breeding is affected by weather extremes, temperatures too low or too high will reduce often reduce breeding success. As will disease, new members to the breeding harem and stress. Females will have up to 20 young usually between 5 – 15, which usually decrease over time. Weaning takes place from 21 days to 25 days.

Males mature slightly later than females. Males are typically placed into breeding at 6-8 weeks of age. The age male mice are weaned may affect their ability to successfully mate, and some groups recommend weaning inbred male mice intended for breeding at 28 days to improve their reproductive performance

Typically, males can breed successfully longer than females as spermatogenesis continues throughout life. However, many male mice tend to become overweight with age, which may negatively affect their ability to successfully breed. It is often recommended to retire and set up new males on a rotating basis such that the average age of the breeding mice does not get to old and general production of the colony suffer.


It is vital you check relevant laws and animal welfare codes in your relevant state. Having been involved in various Animal Houses, I have been trained to euthanase various species and have adapted to do so efficiently.

LIVE MICE should never be offered to reptile except in limited circumstances. Yes I know what if or but my. I have been around long enough worked with the majority of reptiles available and yes some reptiles will need some serious convincing to eat dead food or freshly killed mice.

However in 90% of cases they will eat dead food. As animal lovers treat all animals with respect of course we have to kill numerous thousands of food animals but do it responsibly and with care.

It is difficult for some herpetologists to euthanse either being uncomfortable or less confident. It however is no excuse to feed live prey instead. Seek help on the topic from other breeders.

LIVE MICE should never be offered to reptile except in limited circumstances. Yes I know “What if” or “But my ….”

Key Points for Culling

  • Do not hesitate during a procedure
  • Use dead animals to practise culling
  • Cull in a separate room
  • Store culled mice in the freezer

Presentation / Offering Food

So how do you feed your animals, mice when thawed should be offered to snakes with tongs not your hand this is a safety issue as snakes can strike your hand because its is an extension of the food or because they are excited.

Mice are best kept frozen for at least 4 weeks this usually kills any harboured disease or parasites. Thawing mice is best done either by leaving in the fridge overnight then placing in a warm area maybe on top of reptile enclosure at heat source end. Wait necessary time till the mice are thawed completely an should be noticeably warm. By placing mice in “Luke” warm water and occasionally adding hot water till mice have thawed and become warm to touch. Microwaves are a risky thawing method because like a pie the animal can be excessively hot inside yet feels cool on the outside. This may lead to regurgitation from the reptile.

Mice are often fed on the end of forceps blunt of course, can be thrown into the cage but do not feed with your hand snakes can be a lousy judge of distance when excitable and it can be a painful experience convincing a snake you are not a mouse. Dead food should be jiggled erratically to induce strikes from fussy eaters. Scent them with prey of other items occasionally e. g. Mice can be scented with rats when trying to switch or induce a snake to take rats also.

Obese mice should not be fed in general to reptiles but especially to mature snakes, but if fed at all feed to the younger or growing reptiles. There are numerous reports of snakes that will not eat certain type of mice. For instance your snake may get the same type of white male mouse from the same laboratory for four years but suddenly instead of a white mouse he gets a brown female, this can often be prevented if you offer many colours and both sexes (males are very strongly scented). This also applies for rats, offer small or newborn rats as snake gets large enough to eat them. So that they have had a taste of the larger food source so when they start to grow too big for small food.

Variation of food items is not only good practise in case of a sudden food shortage. It stimulates the snake senses, provides enrichment with added nutritional benefits. Generally baby rabbits, guinea pigs, day old chicks, birds nestlings (domestic), fish are all acceptable alternatives and can be offered to provide a different meal.

When Snakes Refuse To Feed On Mice.

  • Try different rodent sizes, sexes, colours and thawed and freshly killed.
  • Allow time a week to four weeks for a snake to acclimatise to its new enclosure especially you.
  • Ensure the snake is not about to slough (Shed its skin) this is a common cause of refusal to feed.
  • Seasons and timing are also relevant, winter quite few snakes will fast. In spring or other breeding seasons males and females may fast.
  • Sometimes separating snakes if paired or housed together will induce feeding in shy or snakes that are easily intimidated by a larger or more excitable cage mate.
  • Try feeding at night for nocturnal snakes and during the day for diurnal.
  • Scenting mice with fish, rats, birds or lizard faeces or scales (Where legal shed lizard tails can be placed on body or in mouth).
  • Sometimes a trauma e. g. A live mouse attacked or bit the snake when it was young can leave them less inclined to feed on them.
  • Always try using other prey e. g. Rats, guinea pigs, fish, small rabbits, birds etc.
  • Check with previous owner on history or refer to records its feeding pattern.
  • Consult a reptile specialist or veterinarian for help.


Thanks must go to staff at Monash University Lilana Casteneda and Rebecca Cockfield who added comments to the paper.

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