Category Archives: Announcement


Hey its MisterMiceGuy here! Things are really moving foward in my life and I haven’t been focusing on my online content very much the last month or so. Right now I am working on moving so I can start school in the fall. I am also working on doing a bit of rebranding.

Unfortunately I will not be able to keep breeding mice for at least the next 5 years while I am at my university. While this is very unfortunate, I am also excited for the change. I plan of distributing my best mice to various breeders in the new england area so they can use them in their own breeding projects.

Even though I will not be breeding mice after July I am still interested in producing content and animal breeding. Right now I am exploring what types of animals I might be able to work given my situation going forward. Right now I am thinking that it will be some sort of aquatic species such as Guppies or Bettas, or possibly Leopard Geckos.

Originally part of the idea behind MisterMiceGuy was that I bred mice and I was working on becoming a Behaviorist (or I already am maybe?) and typically small animals are used to study behavior. I thought that this connection to behavior might make the term MisterMiceGuy a sort of universal concept for content relating to Behavior and animal breeding. But now I am not so sure.

I really like the name MisterMiceGuy so I would like to keep it but I also don’t want to confuse people if I am no longer breeding mice or posting content specifically about mice. So I am doing some brain storming on ways I can tweek MisterMiceGuy so that I can still use the name but it also reflects my broader interdisciplinary interests.

If you have some suggestions I would love to hear them in the comments 🙂

Observations: Avocado Oil

MisterMiceGuy was exploring increasing fat content in the diet of nursing mothers with the addition of Avocado Oil. “Love Mash” was created using avocado oil instead of cod liver oil. Additionally, Mazuri mouse feed was coated in Avocado Oil before being added to the food hopper.

A nursing female, Dopamine, who was given this Avocado oil coated food was observed with a hunched posture and a messy coat 4 days after giving birth. Additionally, the pups in her litter seemed to have unusually small milk spots. On the 4th day MisterMiceGuy noticed that the mother was aggressively eating only sunflower seeds. Concerned about the haunched appearance MisterMiceGuy tried adding non-oil-coated food pellets directly onto the bedding which the mother immediately started eating.

MisterMiceGuy was not able to find anything saying that Avocado oil was toxic to mice but suspects that Avocado oil makes the food unpalatable.

After uncoated food was supplied the mouse returned to an unhaunch posture later that day.

The Long Hair Genes

Pied Recessive Yellow mouse with long hair (Photo Credit: MisterMiceGuy)

MisterMiceGuy has always been enamored with long haired animals and mice are no exception. In fact is seems that long haired mice are very popular among pet owners and hobby breeders in general (The Finnish Mouse Club 2020). Because of this MisterMiceGuy is incorporating long haired genes into his line of mice.

Illustration of the hair growth cycle in humans. FGF5 protein reduces time spent in the anagen phase and decreases hair length (Photo Credit: Capillus 2017)

There may actually be many genes influencing the length of a mouse’s coat (The Finnish Mouse Club 2020). The gene at play for hobbyist mice seems to be mutations of Fibroblast growth factor 5 gene (FGF5)(The Finnish Mouse Club 2020, HĂ©bert, Rosenquist, Götz, and Marin 1994). Fibroblast Growth Factor 5 (Fgf5) is found on the outer root sheath of hair follicles during the anagen VI phase, which is a phase of hair follicle growth. The FGF5 protein serves to inhibits the elongation of the hair shaft and induces that start of the catagen phase of the hair cycle (HĂ©bert, Rosenquist, Götz, and Marin 1994, and Ota et al. 2002) . In fgf5neo this growth factor seems to be reduced allowing for increased hair length (HĂ©bert, Rosenquist, Götz, and Marin 1994).

According to The Finnish Mouse Club (2020) there is also the Angora gene (go) which appears to be present in the hobby population. Phenotypically it is similar or identical to fgf5neo. Unfortunately as it turns out angora is also recessive a mutant of the FGF5 gene meaning that mice with fgf5neo and fgf5go do not result in augmented hair length when bred together (Hébert, Rosenquist, Götz, and Marin 1994).

It appears that there may be other long hair genes that either are not common or do not exist at all in the hobby population and some of these include, lgh, Fgf5tm1Mrt, skc6, and skc8 genes (The Finnish Mouse Club 2020)

Based personal experience MisterMiceGuy suspects that there are even more additional factors affecting coat length. In mice, coat length reduces with age which may indicate an increased production of FGF5 protein with age. Additionally it seems that there is some difference between guard hairs and undercoat as some mice have very long guard hairs but an average undercoat. Anothing thing that MisterMiceGuy has noticed is that there are differences between hair density which seems unrelated to hair length but effects the overall appearance of the mouse’s coat.


Capillus (2017) Understanding Hair Growth Stages. Retrieved from:

Hébert, J., Rosenquist, T., Götz, J., and Marin, G. (1994) FGF5 as a regulator of the hair growth cycle: Evidence from targeted and spontaneous mutations. Cell, (78)6, 1017-1025.

The Finnish Mouse Club (2020) Varieties. Retrieved from:

Ota, Y., Saitoh, Y., Suzuki, S., Ozawa, K., Kawano, M., and Imamura, T. (2002). Fibroblast growth factor 5 inhibits hair growth by blocking dermal papilla cell activation. Biochemical and Biophysical Research Communications. 290(1), 169-76.

Project Proposal: The Effect of Mint (Mentha piperita) on Habitat Choice in Pill Bugs (Armadillidium vulgare)

[Student’s name’s redacted]


Arthropods are common pests that can be abundant and bothersome inside the household. As such, many people seek out natural insect repellent that won’t be harmful to the environment. The mint plant is commonly suggested as an insect repellant by nonscientific sources and essential oil companies despite mixed evidence to support that claim (Cloyd, Keith, Kalscheur, & Kemp 2009; Koc, Oz, & Cetin 2012). This experiment seeks to test the validity of essential oil claims by investigating mint’s potential to deter pill bugs (Armadillidium vulgare).

Previous research supports the idea that arthropod behavior can be altered by external scents (DrahokoupilovĂĄ & Tuf 2012). DrahokoupilovĂĄ and Tuf (2012) investigated the effects of external marking on the behavior of pill bugs. Nail polish, queen-bee marking, and a non-marked control group were used to mark the insects in various ways (DrahokoupilovĂĄ & Tuf 2012). After marking, exploring, resting, feeding, and hiding behaviors were observed for 24 hours (DrahokoupilovĂĄ & Tuf 2012). Although there was no difference in the survival of marked individuals, large behavior differences were found (DrahokoupilovĂĄ & Tuf 2012). Marked individuals displayed hiding behavior for much longer periods of time compared to the control group (DrahokoupilovĂĄ & Tuf 2012), which provides evidence to support the potential for scents to alter the behavior of pill bugs (Armadillidium vulgare). 

When it comes to the scent of mint, pure peppermint oil has been found to act as a repellent to certain arthropods, such as mosquitos (Koc, Oz, & Cetin 2012). To evaluate the repellant effect of mint on mosquitos, researchers Koc, Oz, and Cetin (2012) utilized hydrodistillation to create essential oil out of the above-ground portion of air-dried mint plants. They placed mosquitos and the mint oil in a glass Y-tube to test the behavior of the mosquitos when exposed to the oils (Koc, Oz, & Cetin 2012). One arm of the Y-tube contained 20 microliters of oil, and the other arm functioned as a control, containing nothing (Koc, Oz, & Cetin 2012). Female mosquitoes were placed in the final branch of the Y-tube, and were left in the device for 30 minutes (Koc, Oz, & Cetin 2012). The insects were observed and their preference for one of the Y-tube arms was recorded (Koc, Oz, & Cetin 2012). The mosquitos showed a high level of aversion to the arm containing the mint oil, indicating that the mint had a strong repellent capability.   

Previous research indicates both that pill bug behavior can be altered by nearby scents, and that mint oil can potentially repel insects. This experiment will combine this previous research to determine the effectiveness of crushed dried peppermint leaves as a natural deterrent to pill bugs. We hypothesize that whole crushed dried peppermint will serve as a natural repellent to arthropods.  We predict that when placed in a choice chamber pill bugs will move away from the peppermint leaves. In our experiment, we predict that placing peppermint oil in a habitat will act as a deterrent, causing pill bugs to avoid the oil.

Materials and Methods

  • Pill Bugs, Armadillidium, Living, Pack 12 (from Carolina supply)
  • One Choice Chamber
  • 8 Quarts EXO-TERRA Plantation Soil Terrarium Substrate 
  • Exo Terra Faunarium, Flat Home 14 inches long x 8 inches wide x 6 inches high
  • 2.2 ounce Tetra TetraFin PLUS Goldfish Flakes with Algae Cleaner Water Formula
  • Driew Plant Mister, Fine Mist Spray Bottle for Cleaning Solution Gardening Trigger Water Empty Sprayer 10oz (Black)
  • 8 ounce Crushed Peppermint Leaves (Mentha piperita)
  • Leaves and Twigs
  • Coronavirus sample

Twelve Armadillidium vulgare will be stored in a faunarium with an inch of plantation soil on the bottom with leaves and twigs to cover the soil surface. This will serve as the crustacean habitat while the bugs are not in the choice chamber. The pill bugs will be fed daily with a spoon full of fish flakes and misted with tap water to keep the habitat moist. The faunarium will be stored in the [Redacted] animal prep room with a cover to keep them dark. The choice chamber will be set up with moist plantation soil in one chamber and  crushed peppermint leaves mixed with moist plantation soil in the other chamber. The pill bugs will be placed in the choice chamber one at a time in the middle of the two chambers to avoid providing bias to the bugs. Each bug will be given two minutes to move towards one side of the choice chamber. The chamber they move to will be considered the preferred habitat. If the bugs do not go towards a side they will be placed back in the housing habitat while the rest of the Armadillidium vulgare are in the choice chambers, then retested at the end with the same protocol. The bugs will test in no particular order, but will be separated after choosing a chamber to ensure no duplicate data. 

Data Collection and Analysis 

The data will be collected by using table 1 to tally how many pill bugs choose each side of the choice chamber. The results will then be analyzed using a T-test to compare the two variables of plantation soil alone or plantation soil with crushed mint. The results will be interpreted using a bar graph to show how many of each outcome occurred.

Plantation Soil
Plantation Soil with Mint
No Choice (Retest)
Behaviors not Listed above

Table 1: Count of possible behaviors occurred

Potential Outcomes

If the pillbugs, all or majority, move towards the plantation only soil this will confirm that mint deters the crustaceans.  In the case that all or most of the bugs move towards the soil with crushed mint, this would conclude that the bugs prefer a habitat with mint scent, oil, or other characters of the mint leaves. The bugs could also be placed in the choice chamber and not move from where they are placed, roll into a ball, or explore the chamber without going to a side. This would give no data to the type of habitat the Armadillidium vulgare prefers in regards to mint.


Cloyd, R., Keith, S., Kalscheur, N., & Kemp, K. (2009). Effect of commercially available plant-derived essential oil products on arthropod pests. Journal of Economic Entomology, 102(4), 1567–1579.

Koc, S., Oz, E., & Cetin, H. (2012). Repellent activities of some labiatae plant essential oils against the saltmarsh mosquito ochlerotatus caspius (Pallas, 1771) (Diptera: Culicidae), Parasitology Research, 110, 2205-2209. 

Drahokoupilová, T., & Tuf, I. (2012). The effect of external marking on the behaviour of the common pill woodlouse Armadillidium vulgare. ZooKeys, 176, 145–154.

Food Quality and Vigilance Behavior in Birds

[Student names redacted]

This is an assignment I worked on as part of a group for a Behavioral Ecology class. Unfortunately we weren’t able to observe any actual birds! See our results below 😩


Birds are known to display vigilance behavior while foraging, though the role of food quality in vigilance levels are unknown. We observed specific vigilance behaviors at three feeders each containing a different food type: sunflower seeds, suet, and dried mealworms. No birds visited the feeders during observation times, though the food left out showed signs of being foraged throughout the week. Despite having equal access to all three food types, sunflower seeds were the food most eaten and the mealworms were barely consumed at all.  Our observations suggest a preference for sunflower seeds over dried mealworms, however no data on vigilance behavior was able to be collected.


     Vigilance behavior in animals is traditionally understood as being a tool to keep watch for predators, though has been revealed to play an important role in the way social animals gather information about conspecific activity and available food resources (Beckoff 1995). One experiment on vigilance in birds conducted by Fernandez-Juricic, Smith, and Kaclenik (2003), investigated how social foraging species use scanning as a means to collect information about nearby individuals while feeding. Their experiments found that when barriers were placed to block vision while in head-down behaviors, birds spent more time utilizing head-up scanning behavior directed towards nearby conspecifics (Fernandez-Juricic, Smith, & Kaclenik 2003). They also found that head-up posture, which was previously thought to be the primary method of scanning in birds, is only one way birds gather visual information (Fernandez-Juricic, Smith, & Kaclenik 2003). Head-down posture while feeding is also an important aspect of vigilance in birds, and should be evaluated when studying scanning behavior in social bird-species (Fernandez-Juricic, Smith, & Kaclenik 2003). 

Another study on vigilance in birds conducted by Guy Beauchamp (2009) investigated the relationship between antipredator vigilance behavior and food density. His study on sandpipers revealed that when statistically controlling for bird density and position in the flock, looking behaviors were less frequent when in a higher density food patch, suggesting a sacrifice in safety in patches with significant foraging gains (Beauchamp 2009). Food density is positively correlated with flock size, though his research helps provide evidence to support the notion that food density could be a confounding factor in the understood relationship between vigilance and group size, and that food is a factor that can affect vigilance behaviors.

Previous research explores how birds display vigilance behavior towards competitors, and how food may impact the degree of vigilance observed. However, no previous research has been conducted on the effects of food quality on vigilance. This experiment plans to fill that gap of knowledge by investigating whether the quality of food found in the patch will affect vigilant behavior while foraging. We hypothesize that changes in food quality will cause changes in social intraspecific and interspecific vigilance and foraging behavior. We predict that birds will display increased vigilance behavior such as head-up (and head-down) posture at feeding sites that have high-quality food, and reduced vigilance and foraging behavior at feeding sites with low-quality food. 

Materials and Methods

We used three identical 11.8” round, hanging, clear dome bird feeders, three thirty-five inch shepherd hooks, five pounds of dried mealworms, five pounds black-oil sunflower seeds, twelve 11.25oz suet cakes made with rendered beef, corn, milo, wheat, millet, and sunflower seed, and an electronic balance to measure mass of food.

We placed three bird feeders in the [redacted] community garden. The feeders were initially filled with 200g seed, 200g suet, and 150g worms with one food type per feeder. We crumbled the suet before placing it in the feeder to ensure even distribution on the feeding plate and to remove food size as a variable.  The bird feeders were left out for two weeks; the first week the feeders were filled with their respective foods and left out to attract birds to and the second week was used to observe bird behavior at the feeders. We checked on the feeders multiple times in the first week and food was refilled when the feeders had little food left. On Tuesday of the second week we observed the feeders for 3 hours from the bench thirty feet from the closest feeder to record bird behavior. We created an ethogram to record behavior, as listed on the Food Quality and Vigilance Behavioral Data Collection sheet (Table 1). Each time a behavior was displayed, the behaviors were tallied on the ethogram under the section for the corresponding feeder. Some behaviors to observe include: head-up posture, head-down posture, scanning before eating, and leaving the feeder when another bird arrives. 


Bird feeders in the [redacted] Community Garden were observed for 3 hours; in that period no birds were observed feeding at the feeders.  We noted that there were no birds chirping or singing in the area. If data had been collected an analysis of variance (ANOVA) would have been used to compare data points.  We observed Behaviors listed on the ethogram (Table 1) such head up posture, head down posture, multiple different birds landing on the feeder at the same time, scans before taking food, eating at the feeder, leaving with food from feeder, bird leaves when another bird arrives, and other behaviors not specified.  We recorded behaviors at the Sunflower feeder (M=0,SE=0), the mealworm feeder (M=0,SE=0), and the suet feeder (M=0,SE=0). Due to no birds being observed, major trends and statistically significant data were not able to be determined.


Our hypothesis was that birds would display different vigilance behaviors at feeders containing food of varying values. We predicted that birds would show more vigilant behaviors at feeders containing worms, medium vigilant behaviors at suet, and the lowest vigilant behaviors at the sunflower seed feeder. Although no birds were observed at the feeders, we determined that birds preferred sunflower seeds most, then suet, and preferred mealworms least based on the amount of food left in and around feeders. These observations suggest that the high value food item is actually sunflower seeds, however the hypothesis was neither supported nor refuted because no behavioral data was observed or collected. 

There are a number of factors that could have caused birds not to forage during the observation time in this experiment. The location of the feeders could have influenced the birds from coming including the time of day relating to the proximity of a busy road, foot traffic, and other noises such as the nearby playground. The feeders were also in the middle of the garden away from trees or other protections which may have prevented the birds from foraging in the middle of the day. Lastly, the weather could have influenced the birds. The experiment was run towards the end of winter when migratory small birds may not have been present in the area yet, but the birds that were around could have been able to forage elsewhere due to the unusually warm winter and lack of snow cover and frozen ground. 

Additionally, an ornithology professor at Maine’s Colby College has noted that there has been a widespread reduction of birds at feeders in the region recently. He has stated that this may be due to declining bird populations or birds finding an abundance of food in their environment (Wilson, 2020). Further research on the subject should be conducted over a longer period of time in a location with a large bird population. For optimal observation, a camera could be utilized to view behavior at all times of the day without disturbing any of the birds.

Food Quality and Vigilance Behavioral Data Collection Sheet (Table 1)
Feeder typeBehaviorCount
Suet Multiple Birds Land on Feeder at Same Time0
Bird Scans before Taking Food0
Bird Eats at Feeder0
Bird Leaves with Food from Feeder0
Bird Leaves when Another Bird Comes0
Head-Up Posture0
Head-Down Posture0
Other Behavior not listed above0
Sunflower Seed Multiple Birds Land on Feeder at Same Time0
Bird Scans before Taking Food0
Bird Eats at Feeder0
Bird Leaves with Food from Feeder0
Bird Leaves when Another Bird Comes0
Head-Up Posture0
Head-Down Posture0
Other Behavior not listed above0
Food Quality and Vigilance Behavioral Data Collection Sheet (Table 1) Continued
MealwormMultiple Birds Land on Feeder at Same Time0
Bird Scans before Taking Food0
Bird Eats at Feeder0
Bird Leaves with Food from Feeder0
Bird Leaves when Another Bird Comes0
Head-Up Posture0
Head-Down Posture0
Other Behavior not listed above0

Table 1.  Ethogram of behaviors to observe. Bird feeders were observed for 3 hours; however, no birds visited the feeders therefore no behavioral data was collected.


Beauchamp, G. (2014). Antipredator vigilance decreases with food density in staging flocks of semipalmated sandpipers (Calidris pusilla). Canadian Journal of Zoology, 92(9), 785-788.

Bekoff, M. (1995). Vigilance, Flock Size, and Flock Geometry: Information Gathering by Western Evening Grosbeaks (Aves fringillidae). Ethology, 99(1-2), 150–161.

Fernandez-Juricic, E., Smith, R., and Kaclenik, A. (2003) Increasing the costs of conspecific scanning in socially foraging starlings affects vigilance and foraging behaviour.  Animal Behavior, 69, 73-81.

Wilson, H. (2020) Where are my feeder birds?  Retrieved from:

MisterMiceGuy's Guide to the Science Fancy Mouse Breeding


One of my goals as a mouse breeder is to use mouse breeding to help others gain exposure to science and the natural world. I want to encourage and promote realistic animal breeding that’s based on science and I want it to be available to mature and responsible adults interested in these subjects. To accomplish this, I am writing this guide to becoming a fancy mouse breeder.


Mouse pups are cute but there are a lot of things that come with mouse breeding that are not cute. These include witnessing death, cannibalism and euthanasia. It’s not uncommon for a mouse breeder to find a dead mouse who has had its head eaten off by its cute cage mate. It’s also not uncommon to check in on your prized litter only to find that their mother has decided to eat the limbs off all her pups. It’s not for the faint of heart. In addition, there is also the reality of euthanasia. Although some might find it controversial euthanasia is frequently part of a breeding program that is carried out by the breeder themselves. This can be emotionally daunting, but some breeders feel it’s a necessary part of the hobby (Royer 1998). If you’re prepared to accept the realities of mouse breeding, then maybe you’re ready to explore mouse breeding as a hobby.



First thing you will need are appropriate cages for the mice and a place to keep those cages. If you plan on breeding multiple generations of mice you will need multiple cages to support a small colony of mice. Mister Mice recommends a minimum of 4 cages. One to house your breeder male, one to house a female with pups, and two to grow out your pups.

Some mouse breeders make their own cages out of large plastic bins by adding wire mesh to the sides and lid for ventilation.  Suitable plastic or glass cages can also be purchased but hamster-style cages are not recommended (FMBA 2019).  You can find instructions to make these online.  Remember that good cage ventilation is important as this helps reduce the buildup of toxic ammonia fumes (Smith, Stockwell, Schweitzer, Langley, & Smith 2004)

Recommended cage sizes for mice is based on the size of the mouse with larger mice needing larger accommodations. For Mice being housed in groups it is recommended that a 25g mouse have a minimum 15 sq. in. of floor space. The minimum height for a cage is for mice is 5in. The minimum floor space for a mother with pups is 51 sq. in. (National Research Council 2010). To figure out the size of your cage multiply the length (in inches) by the width (in inches) and that will give you total square inches.

You will also need a place to keep these cages. MisterMiceGuy suggests using a wire utility shelf or similar shelving system. The shelves can be adjusted so you have plenty of space to house your mice on top and then you can have space on the bottom to house your mouse supplies such as bedding or food.


Mice prefer beddings that contain large fibrous pieces (Blom, Van Tintelen, Van Vorstenbosch, Baumans & Beynen 1996). However not all large piece beddings are created equal. Untreated softwood beddings have been shown to affect the immune system and Cedar bedding has been associated with tumor development, altered liver enzyme functioning, and cytotoxicity in mice (Vlahakis 1977, National Research Council 2010 and Sabine, Horton, & Wicks 1973). Fancy Mice Breeders generally avoid cedar and other soft wood beddings (FMBA 2019). However, Kiln-dried pine maybe used as the kiln drying process reduces the aromatic hydrocarbons that are found in untreated pine. Special precautions should be taken regarding bedding used for hairless mice as their lack of eye lashes may contribute to conjunctivitis (Research Council 2010).

It’s worth noting that research has compared the ability of different beddings to control ammonia levels. This is relevant because ammonia is associated with disease in mice (Mexas, Brice, Caro, Hillanbrand, & Gaertner 2015). They found that the common paper-based bedding “Care fresh Ultra” performed significantly worse in controlling ammonia levels when compared to pine shavings, hardwood, or corn cob bedding (Smith, Stockwell, Schweitzer, Langley, & Smith 2004). Hardwood beddings, such as aspen shavings, are thought to be the best wood-based bedding for mice and are very good at controlling ammonia levels (FMBA 2019 and Smith, Stockwell, Schweitzer, Langley,& Smith 2004). It is common practice to replace bedding and sanitize cages weekly however some fancy mouse breeders recommend twice weekly cleanings (Mexas et al. 2015, AFRMA 2019)

Food and Water

Water bottles designed for small animals should be used to supply fresh water. Commercial “Lab block” style products designed for mice or rats can be used for food. Some breeders create their own food mixes (FMBA 2019). However, care should be taken as inappropriate macro nutrients, such as too little protein can have adverse effects on mice (Watkins et al. 2008).


When it comes down to it you have basically two options when it comes to getting animals to start with: pet store or private breeder. It’s common to find mice at pet stores but the quality of these mice can be lacking. It’s likely that these mice will have poor body types and poor temperament. You want to look for mice with broad heads and large ears in the coat color that you want. You will save a lot of time by starting off with a male that has the basic coat type and color that you want or that has exceptional type.

The preferred method is starting off with mice from a private breeder. You can locate private breeders on one of the fancy mouse breed club pages or by doing a google search. Again, its best to start with a male that closely matches the color and type that you are looking for. By purchasing from a breeder not only will you be starting off with higher quality animals but it’s likely that the breeder will know the genetic history of your animals. This can be useful if you have specific breeding goals.


Grasp the mouse by the tail near its base and place the mouse on a surface, such as your palm, that it can grab while maintaining your firm but gentle grip. Young mice should be picked up by scooping your hands around their entire body, or by picking up a group of baby mice along with some nesting material (Connor 2007).


Breeding mice is straight forward. Mice are old enough to breed between 4-7 weeks of age. Pregnancy in mice lasts 19-21 days. Once mice are born, they will wean off their mothers milk in about 21 days. Litter sizes vary from small litters of 4 pups to large litters of 12 pups. A female mouse’s breeding life span is from 6 to 12 months, and total life span can be anywhere from 1 to 3 years (Connor 2007).

Female pups should be separated from their male siblings and father between 3 and 4 weeks of age. If they are allowed to remain longer, they may become pregnant. Female mice that are bred before 6 weeks of age are still immature and may have difficulty giving birth or be more likely to eat her offspring. Additionally, females may start to loose fertility after about 6 months of age (Connor 2007).

When pairing mice you should make note of the pairing by documenting the pair, the date of the pairing, the estimated date of birth (Connor 2007). Once the pups are born you can go back and note the 3 week date and the 6 week date so that you know when to separate the pups and when they can be breed. Mister Mice suggests keeping a small note book for this purpose called a Breeder’s Log.

When caring for a pregnant mouse a higher fat diet may be provided for milk production. Handling of the female should be avoided for the first day or two after birth as this may cause the mother to eat her pups. Actually, any stressful events such as noises, aggressive handling, or overcrowding can lead to decreased fertility and increased chance the mother will eat her pups (Connor 2007).


When selecting mice to breed it’s important to have a goal in mind.  Ask yourself what do I hope to achieve with this pairing?  Generally speaking, there are two basic methods of selecting pairs.  One is that you pair animals with similar trains with a goal on improving that trait.  For example, you pair your largest eared mouse with your largest eared mouse with the goal of producing even larger eared mice.  The other method is pairing animals based on the traits that they don’t have.  For example, you have a large eared mouse with a narrow head, and you breed it to a mouse with a wide head but small ears with the goal of producing a mouse with a wide head and large ears or at least reducing what you feel is a fault in that mouse. 


There is a difference between breeding a pair of mice and breeding a line of mice. In order for your mice to “breed true” you need to develop a line of mice the consistently produces mice with the desired traits. If this is your goal, then you need think about setting up a breeding plan (Greenwood-Dudar 2018).

The first step is to identify the traits that you want to see in the mice you are producing (Greenwood-Dudar 2018). Traits can include any of the observable physical or behavioral characteristics (Barber 2005 and Genetic Learning Center 2016). If you plan on showing mice you might want to familiarize yourself with the varieties of mice and the characteristics associated with them (FMBA 2019, AFRMA 2019, and Greenwood-Dudar 2018). The second step is developing a feel for what those traits should look like in your mice. This includes being able to evaluate a given mouse and determine if it has the traits you are looking for (Greenwood-Dudar 2018).

As a new breeder you can increase your knowledge in these areas by joining a mouse breeders club, contacting local mouse breeders, or reaching out to other breeders on social media. If there are mouse shows in your area attending those might be helpful (Greenwood-Dudar 2018).


Growth: Mice develop rapidly between birth and 4 weeks and you will notice daily changes. On days 3-4 the ears will lift away from the head. On day 6-7 a coat of fine fuzzy fur starts to grow. On 9 day nipples are visible on females only. On days 10-11 their teeth break through their gums. On days 12-14 their eyes will open (Connor 2007).

Weaning: At about 3 weeks old mice will look a lot like tiny adults and will be ready to eat solid foods. If pups are separated too early from their mother, they may die so it’s important to know they are eating on their own before separation. One wat to test this to observe the pup’s behavior when you remove the lid to their cage. If the pups lay still, they are too young. However, if they run or jump around the cage then they are old enough to be separated (Connor 2007).


If you are a member of a mouse breeding club then take a peak of the club’s “standards” to see the traits that are desirable in show mice.  These are the traits you want to select for.  It might be helpful to google show mice to get an idea of what show mice look like.

There are two different stages in which mouse selection occurs.  Once when the mice are pups and another time when the mice are adults.  When the mice are adults it should be easier to tell if they have the traits you are looking for.  When you have a new litter it can be hard to tell if the mice will have the traits you are looking for.  Usually when selecting pups out of a litter you want to look at the width of the pups head and overall size of the pup.  Unfortunately, there are some traits (such as angora) you just won’t be able to select for until the mice have matured. 

Sex is also an important trait you want to pay attention to.  Male pups cannot be bred back to their father and they will fight with other males so breeders will often cull all their male pups. In fact, any pup that is small, sickly, or doesn’t have the traits you want needs to be culled from the breeding program.


Culling is simply removing an animal from your breeding population. It is sometimes divided into Hard Culling and Soft Culling. Hard Culling refers to euthanizing ill or unwanted animals. Soft Culling refers to removing of the animals by re-homing or by simply not using them in your breeding program any longer.

It would be nice if all the mice you produce were healthy and you could find homes for them. However, the reality is that mice produce far more offspring that you could possibly rehome. Additionally, in the wild most of these individuals would not survive. This high mortality rate in the wild is why mice produce so many offspring. In the captive breeding environment this makes culling a useful tool for the breeder.

There are two acceptable means of culling are Carbon Dioxide (CO2) for adult mice and Hypothermia for mice under 7 days old. The best way of using CO2 is by means of compressed gas cylinders as this allows you to regulate the flow of gas. Its preferable that mice be euthanized in their home cage but if not, a clean cage should be used (AVMA Guidelines 2013). Some breeders create their own CO2 gas using citric acid and baking soda. A 2-liter soda bottle system designed for aquarium CO2 injection might be used. Additionally, some breeders use CO2 cartridges and valves designed for brewing. (NEED CITATIONS)

Hypothermia is an acceptable means of euthanasia but only for mice under 7 days old (aka pinkies). This is because baby mice do not produce their own body heat. Death by hypothermia can be achieve by gradual cooling in a refrigerator. Mice should not be placed directly on cold or pre-cooled surfaces as this can cause tissue damage and potentially pain (AVMA Guidelines 2013).

Some mouse breeders cull unwanted pinkies in the belief that the pups that remain are healthier (Royer 1998). Research has indicated that pups from unculled litters have a reduced weight of 4% but that this difference disappears by 3 months of age (Paigen, Marion, Stearns, Harper and Svenson 2014). Additionally, some breeders believe that culling the males (which are larger) and leaving behind females will produce larger healthier females (Royer 2014).


There are many factors involved in being an ethical breeder (Royer 2015) Being an ethical breeder involves being concerned with animal welfare. Animal welfare is allowing animals to be healthy, comfortable, safe and free from fear and pain among other things (American Veternary Medical Association 2019). Being an Ethical Mouse Breeder involves breeding animals that are selected for traits that improve the health and appearance of animals and not breeding sickly individuals. It involves humane euthanasia of unwanted animals and using those animals in some resourceful way such as for food or education. Please see my article on Animal Welfare for more information on this topic.


Once you’re setup with your mouse breeding program you might consider joining a Fancy Mouse Breeders Club.  This will allow people to find you as a breeder, puts you in contact with other breeders, and allows you to find and participate in mouse showing competitions.  Two common clubs in the US are the Fancy Mouse Breeders’ Association and the American Fancy Rat & Mouse Association.  When you join one of this clubs you will select your official breeder name.

In addition to Joining a club you will want to setup a simple website, facebook, Instagram, or other social media account for your mice.  It can be simple with your contact information and location.  It should also describe the types of mice you are working on.


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American Veterinarian Medical Association (2019). What is Animal Welfare? Retrieved from:

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Mexas, A.M., Brice, A.K., Caro, A.C., Hillanbrand, T.S. and Gaertner, D.J. (2015) Nasal histopathology and intracage ammonia levels in female groups and breeding mice housed in static isolation cages. Journal of the American Association for Laboratory Animal Science54(5), pp.478-486.

National Research Council (2010) Guide for the care and use of laboratory animals. National Academies Press.

Paigen, B., Marion, M.A., Stearns, T.M., Harper, J.M. and Svenson, K.L., 2014. The effect of culling on health and physiology of mouse litters. Laboratory animals48(3), pp.207-215.

Royer, N. 1998. Culling: The question that has plagued the fancy for many years. American Fancy Rat and Mouse Association. Retrieved from:

Royer, N. 2015. A Responsible Breeder’s Code of Ethics. American Fancy Rat and Mouse Association. Retrieved from:

Royer, N (2014) Culling: The question that has plagued the fancy for many years. American Fancy Rat and Mouse Association. Retrieved from

Sabine, J.R., Horton, B.J. and Wicks, M.B., 1973. Spontaneous tumors in C3H-A vy and C3H-A vy fB mice: high incidence in the United States and low incidence in Australia. Journal of the National Cancer Institute50(5), pp.1237-1242.

Smith, E., Stockwell, J.D., Schweitzer, I., Langley, S.H. and Smith, A.L., 2004. Evaluation of cage micro-environment of mice housed on various types of bedding materials. Journal of the American Association for Laboratory Animal Science43(4), pp.12-17.

Vlahakis, G., 1977. Brief Communication: Possible Carcinogenic Effects of Cedar Shavings in Bedding of C3H-Avy fB Mice. Journal of the National Cancer Institute58(1), pp.149-150.

Watkins, A., Wilkins, A., Cunningham, C., Perry, V., Seet, M., Osmond, C., Eckert, J., Torrens, C., Cagampang, F., Cleal, J. and Gray, W. 2008. Low protein diet fed exclusively during mouse oocyte maturation leads to behavioural and cardiovascular abnormalities in offspring. The Journal of physiology586(8), pp.2231-2244.

Genetic Learning Center (2016). Inherited Human Traits: A Quick Reference. University of Utah. Retrieved from:

Barber, N. (2015) What Behaviors Do We Inherit via Genes? Psychology Today. Retrieved from:

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MisterMiceGuy Tries Out New Laboratory Cages

So far MisterMiceGuy has used 10 gallon glass aquariums and extra large plastic critter carriers with a modified lid to house his mice. Recently MisterMiceGuy acquired 5 mouse lab breeding cages from Reptile Basics Inc. The cages are made from durable High-density polyethylene and have a 1/4″ stainless screen top with accomodations for food and water. Each cage can accommodate 1-3 mice (Reptile Basics Inc. 2020). As March 20, 2020, two of the cages have been in use for 11 days.

Mouse breeder cage from Reptile Basics Inc. (Photo Credit: Reptile Basics Inc. 2020)

Initially MisterMiceGuy was reluctant to use laboratory cages due to the cost of each enclosure and the opacity of the cage. However, after using them MisterMiceGuy regrets not having invested in laboratory style cage from the beginning.

In the new cages the plastic water bottle rests above the cage lid out of reach of the mice, minus the metal water dispenser part. Prior mice had full access to the entire plastic bottle. This resulted in the bottle occasionally being chewed through and the mice periodically experiencing stressful periods without water. MisterMiceGuy has noticed that mice deteriorate very quickly without access to water. The new cages eliminate that problem allowing mice access to continual clean water without periods of dehydration. This also reduces costs incurred by replacing plastic water bottles that have been chewed through.

Secondly the new cages have a food hopper built into the lid. This keeps the food from being contaminated in the bedding and allows it to be dispensed as needed. Prior the food was distributed on to the bedding. Although foraging for food can be beneficial to mice (Lecker and Froberg-Fejko 2016), this meant that the food would be soiled with urine and faeces. Additionally the food would quickly disappear into the bedding making it difficult to determine how much food when the food had run out. The resulted in periods were food was wasted or periods were mice may have been underfed. The new cages eliminate these problems by keeping the food uncontaminated and easy to view and resupply.

The cages are also lightweight and very easy to clean. Now that the food isn’t being mixed into the bedding and the water bottles arn’t being damaged the bedding staying cleaner longer and less bedding is used over all. 10 gallon glass tanks are fragile, cumbersome and difficult to clean and MisterMiceGuy does not recommend them for this reason.

MisterMiceGuy has observed improved overall appearance of the mice kept in the new cages. So far MisterMiceGuy highly recommends investing in laboratory style cages for the serious hobby breeder.


Reptile Basics Inc. (2020) Mouse Breeding Cage. Retrieved from:

Lecker, J., and Froberg-Fejko, K. (2016) Using environmental enrichment and nutritional supplementation to improve breeding success in rodents. Bio Serv, 45(10), 406-407.