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Care of Mice and Rats

Care of Mice and Rats

Mice are rats are not the same species, yet for general care they are very similar.  Mice and rats are an omnivore, which means they can eat everything from insects and plants to meat.  A main problem we see is malnutrition from feeding a hamster diet to rats and mice.  You should feed a diet labeled for mice or rats.  A diet labeled for hamsters, gerbils, mice and rats is usually not a quality diet and should be avoided.  Hamsters and gerbils are herbivores, which indicate they eat only plant materials.  Feeding dogs a grass hay diet is a similar comparison of why carnivores and/or omnivores cannot survive on plant material alone.  Rodent diets containing seeds indicate a poor quality product; the pelleted diets are much superior.  If you cannot find a rodent diet, then a dry cat or dog food with 16% or more protein is adequate.  On a complete pet diet vitamins are not required.    Obesity is a problem in our pets, including rats and mice.  Up to 10% of their diet can also be human food, which should be fruits, vegetables, grains, yogurt and some cooked meat without fat.  Candy, sugar, chocolate and similar treats are to be avoided.  As a general rule rodents and other pocket pets should not have seeds or especially fruit as over 5% of their diet.  Feeding out of a hopper system is adequate for adult rodents.  The baby rats or mice need an additional low profile tray or bowel on the cage floor to eat out of.  Water bottles are adequate for adults, yet we recommend you also have a shallow bowl of water available for the babies.  Daily look to ensure there are new stools and that water is being consumed, especially if using a water bottle.   

            In the wild rats and mice are usually active at night (nocturnal), but in captivity they are more active during the daytime.  The first rats became domesticated in the 1800‘s.  Both species are usually gentle, although they may bite if provoked or handled improperly.  The teeth of mice, rats and other rodents continually grow throughout their life.  Some rodents need their teeth trimmed periodically. 

            Housing should be a commercial cage, which should be designed to be escape proof.  There should be no sharp edges and a solid floor.  Wire flooring can cause feet and other problems.  Plastic, wood and glass make adequate habitats, since these surfaces are easy to clean.  Wood will be chewed up by rodents.  Periodically the habitat should be cleaned with a disinfectant, such as a peroxide disinfectant that we have available.  For rats we recommend a cage that is at least 12” high.  A hiding box, where the mouse or rat can get away from human view, is required inside.  Animals need a space to hide and relax.  Rats like to also burrow under things and we recommend that you provide a towel for this purpose.  Tubes, boxes, exercise wheels and other toys can be provided, as long as they are constructed of safe to eat materials (cardboard) or indestructible materials.  Soft rubber is to be avoided if the rodent chews it up.  When cleaning the habitat use a 1/30 chlorine bleach solution, water rinse, wipe down and then allow to air dry before reintroducing them back into their habitat.  If a rodent escapes, and especially if you have pet cats or dogs, we recommend you close up the room and call us for rental of a humane trap.  Rats usually will go back into their cage, but mice usually will not.  Temperature extremes, noises, vibrations and other similar stresses should be avoided.

            In Colorado it is illegal to use aromatic wood shavings within pet shops selling rodents.  Redwood, cedar and other such shavings release oils that can create problems.  Pneumonias are seen in rodents, ferrets and other small pets housed with aromatic wood shavings.  (The stores can sell these shavings but cannot use them).  Wood shavings from non-kiln dried pine can also cause problems; some pine shavings are okay while some other freshly chipped pine shavings can cause problems.  We recommend aspen wood shavings if any.  Newspaper, shredded paper or even commercially available corncob products (processed) are preferred.  The bedding should be changed 2-3x a week, as the rodent’s lungs are sensitive to the ammonia from urine build up. Vinegar may be needed to dissolve urine scald.  Mice have a stronger urine smell than the other rodent species.  There is nothing that can be done to remove this natural odor.  Masking it with cedar bedding causes a pneumonia.  Wood chips seem to hold the odor longer, and thus for mice a newspaper or compressed chips made of newspaper is recommended along with daily changing of all the bedding.  There are also odor eliminators with enzymes, which help remove the odor when one is cleaning up the habitat.  Always double rinse and dry any habitat when using cleansers.  If you compost your rodent’s bedding we recommend a lungworm test of the feces.   We recommend that on average you do not compost your rodent or reptile shavings/bedding.    

            The life expectancy of a rodent is 1-2 years for mice and 2-3 years for rats.  If they live longer than 2 years of life they can have a 2/3+ chance of developing cancer.  Usually we notice skin tumors, yet leukemia can even be found in mice.  Mice & rats have a higher rate of cancer than humans do.  We recommend that if you find a mass on your mouse or rat, especially near her teat area, it be removed while it is small in size.

            Pneumonia is common in rodents, especially if housed in an environment with aromatic wood chips and/or urine smell.  Mycoplasma, or Chronic Murine Pneumonia (CMP), is common and can also affect pregnancy.  To help keep out mycoplasma one can go to a 2 month quarantine period for all new additions.  One also should house mice and rats far away from other carrier animals of Mycoplasma (rabbits, guinea pigs and other rodents).  Clostridium piliformis (Tyzzer’s disease) can cause weight loss, diarrhea and sickness in mice, and sometimes rats, gerbils (and raccoons, horses, etc; Bacillus piliformis is the old name for this toxic bacteria).  Although Clostridium can be found in food and water, Gerbils can also transmit and die from Tyzzer’s disease.  Wet tail is a common name for diarrhea in rodents, and has many causes, such as Campylobacter.   Bubonic Plaque is found in the prairie dogs colonies in our area, but not in domestic rodents.  Corona hepatitis in mice, mouse pox, mouse rotavirus, Sandia virus, Sialodacryoadentisi virus and other diseases can also be found, usually diagnosed by a necropsy.

            Internal parasites, such as pinworms and tapeworms, can be found in rodents.  A periodic fecal exam of all animals is recommended; a lungworm test once is recommended on all rodents.   Lice and other external parasites can also occur.

            A phenomenon we sometimes see in rodents and ungulates (cloven hoofed livestock) is chromodacryorrhea.  Chromodacryorrhea is a medical term for red tears.  This redness is from a chemical poriphorin secreted from the animal’s harderian glands near the eye.  Porphyrin will fluoresce under a black light, while blood will not.  Chromodacryorrhea can be due to sickness or a response to stress. 


            Rats are of the species Ratttus norvegicus, and originally came from central Asia.  Cage territoriality can be a problem with some rats.  If one has such a problem it can be overcome by picking up the rat outside of its territory.  Take a clear plastic tube and Plexiglas plate to cover the door and direct the rat to another habitat area for catching.  Overall rats live in a group setting more than mice do.  Other females in the group can raise some of the rat babies in a communal effort.  Since cannibalism can occur, we recommend keeping the male rat away from the females.  To pick up a rat grab them over their back to lift.  Picking them up by the tail is not recommended. 

            A female rat comes into estrus (heat) every 5 days year around (polyestrus).  After breeding a white plug may be noticed, and this is normal.  Gestation (pregnancy) is about 22 days, with approx. 9 pups in a litter.  For the first weeks the mother should not be stressed, examined or played with.  Her hiding box should be left untouched.  An upset mother may become cannibalistic.  After the babies are weaned in 3 weeks she will go back into estrus and can become pregnant within a week.  Rats should not be bred until they are 2.5-3 months of age.  We recommend castrating the male rats at 90 days of age and/or approximately 200 grams body weight.

            The diseases of corona virus, parvovirus, ileitis, typhilits or Tyzzers (Clostridium), mycoplasma are fairly rare in rats, as are the cancers of fibroadenoma and granular lymphocytic leukemia (Fisher Rate Leukemia).


            Mice also originated from central Asia.  The most common strain of Mus musculus is the Swiss Albino.  The social hierarchy causes a male to usually be dominant over the rest of the pack.  In a group setting of limited space we recommend separating pregnant females, as they will fight to defend their nest.  It is estimated that a single pair of mice can have 1 million descendents in 1.5 years, if the conditions are right.

            Mice kept singly appear to bite more than those housed in groups.  Even with this knowledge we do not recommend getting a 2nd mouse because of the potential breeding problems.  Sexing rodents can be done, yet this can be difficult when they are very immature.  Picking up a mouse by its tail is not a problem, and sometimes preferred.  If you need to hold them tighter just grab and hold them by a simple pinch hold to the back of the neck. 

            If housing more than one mouse together, females are best kept in a group unless they have babies.  Males usually are best kept alone, as they have a tendency to fight other males and sometimes the females.  Barbering is a term used when one mouse starts chewing the hair off a cage mate, and the separation of these two mice is then indicated.  A male with multiple females is usually adequate for a breeding situation.  A female mouse can come into estrus (heat) every 5 days year around.  Her gestation period (pregnancy) is approximately 20 days, and there are 5-12 pups (babies) on the average.  Younger and older mice or rats may have smaller litters.  Leave the mother and babies alone in their private box.  Do not upset the mother for the first week after birthing, or she may become cannibalistic.  A newborn mouse can become pregnant after one month of age.  If you want to breed a mouse she should be over 2 months old. 

            The viral diseases of mouse hepatitis virus, Sendai virus (respiratory paramyxovirus), ectromelia virus (mouse pox), arena virus (LCM) are fairly rare in pet mice.  Pasteurella, Mycoplasma, Salmonella, Pseudomonas, Staph, Helicobacter hepatitis and typhlocolitis are also rare, as are the parasites of nemadotidaisis (pinworms), ascariasis (mycoptes fur mites) and pneumocystis protozoan pneumonia.  All rodents have a high predisposition to cancers, such as mammary lymphoma in mice.