Mouse and Rat Care
Cat and Exotic Care of the Central Coast
Maxwell Conn, DVM
565 Five Cities Drive
Pismo Beach, CA 93449
Ph: 805-773-OCAT (773-0228)
Fax: 805-773-0229
www.catandexoticcare.com
Full Service Hospital & boarding for Cats, Birds, & Small Mammals
People have many differing opinions when it comes to rats and mice. Some
consider them as vermin or pests, many envision them as laboratory animals, others think
of them as snake food, while a chosen population treasure them as pets. If properly cared
for, these small rodents (especially rats) make excellent pets. When hand-reared with
care, rats seldom bite. These timid, yet social pets, are fun to watch while performing
their natural behaviors of running, burrowing, searching for food, and playing. Unlike
their wild counterparts, which are largely nocturnal, pet rats and mice have periods of
activity both during the day and night. They are inexpensive, easy to care for, and
responsive to handling and socialization.
DIET
As with any pet, good quality food and clean fresh water must be provided at all times.
In the wild these animals feed on leaves, seeds, roots, fruits, snail, slugs and insects.
Pelleted rodent rations are recommended as the main food source for captive mice and
rats. These are processed as dry blocks or pellets. Typical maintenance diets contain
about 14% protein and 4-5% fat. Diets for growth and reproduction contain 17-19%
protein and 7-11% fat. There are commercially available seed diets that are formulated
for mice and rats, but these diets should only be used to supplement the basic rodent
pellet (as a treat item). Rodents prefer sunflower seed based diets to pellets, but these
diets are low in Calcium and high in fat and cholesterol. When fed exclusively, seed
based diets can lead to obesity and nutritional deficiencies.
The pet’s appetite should be monitored closely. Many factors affect the intake of
food in a rodent. These include ambient temperature, humidity, food quality, breeding
status, and the pet’s health status. On average, an adult mouse will consume about 15 gm
of food and 15 ml of water per 100 gm body weight (daily). Comparatively, an adult rat
will consume approximately 5 gm of feed and 10 ml of water per 100 gm of body weight
(daily). Rats and mice typically eat at night.
HANDLING
Pet rodents become tame and seldom bite when properly restrained and adjusted to
handling. Be careful, however, when approaching a nervous or frightened pet. It is best
not to disturb a sleeping animal because most are quite cranky when suddenly awakened.
Some rats are very territorial and protective of their cage. These individuals should be
coaxed out of there cage before being handled. Mice housed individually may be more
aggressive and apprehensive than those housed in groups. Once away from their cages,
most pet rats and mice enjoy being handled.
Rats and mice can be easily picked up, by scooping them into a can or cupped hands.
They can then be moved out of their territory into a neutral area. Mice can also be lifted
by the base of their tail. Rats can be picked up similarly, but be careful not to injure them
due to their larger size. For any rodent: never pull on the tip of the tail, because the skin
can easily tear and become stripped from its underlying connective tissue.
A mouse can be further restrained by placing it in a rough or wire surface and grasping
the scruff of the neck using thumb and forefinger. The rest of the body can then be
restrained by trapping the tail between the palm and little finger of the same hand. This
position allows for close examination and treatment.
Rats can be restrained by grasping over the back and rib cage, while restraining the head
with a thumb and forefinger positioned on either side of the neck. Initially, it may be
necessary to grasp the tail base as suggested above. Rats do not respond well to scruffing
by the nape as in mice, but it may be necessary for a thorough exam in some cases.
HOUSING
Several types of suitable cages are available for housing small rodents. Many of these
units come equipped with cage “furniture”, including exercise wheels, tunnels, and nest
boxes. These accessories contribute to the pet’s psychological well being. Cages should
be constructed with rounded corners to discourage chewing. Rodents readily chew
through wood and thin plastic. Recommended caging materials include wire, stainless
steel, durable plastic and glass. Glass and plastic enclosures do restrict ventilation and
may lead to temperature and humidity problems. These materials are acceptable when at
least one side of the enclosure is open for air circulation.
Mice and rats do best in solid bottom cages with deep bedding and ample nesting
material. Bedding must be clean, non-toxic, absorbent, and relatively dust-free.
Recycled newspaper pellets, aspen pine shavings, and shredded paper towels are
acceptable beddings. Cedar chips or chlorophyll scented shavings should be avoided due
to implications with respiratory and liver disease. Corn cob hull and rabbit pellet type
bedding materials should be avoided, as this organic material serves as a substrate for
bacteria and fungi to flourish. At least one inch of bedding should be provided to allow
for normal burrowing behaviors. Cotton and shredded tissue paper make excellent
nesting materials.
Adult mice require a minimum floor area of 15 square inches, and a cage height of five
inches. Rats need at least 40 square inches of floor space, and a minimum of 7 inches in
height. Breeding rats and mice require a much larger area. Optimal temperature range
for these pets is between 65-80 degrees Fahrenheit, with a relative humidity of 40-70%.
Twelve-hour light cycles are preferred, with most rodents more active during the night.
Pet rats and mice can be housed singly or in groups. These rodents are colony oriented
by nature. However, occasionally an overly aggressive mouse or rat may have to be
caged alone. Territorial disputes can develop when the cages are overcrowded or when
they lack sufficient food or water. Group cages should be provided with multiple food
and water sources
As a rule of thumb, the cage and accessories should be thoroughly cleaned at least once a
week. An exception to this schedule is when newborn babies are present. In this case,
wait until they are at least 10 days old before cleaning. Other factors that may necessitate
increased frequency of cleaning are number of animals in the cage, type of bedding
material provided, and cage design and size. Cages should be sanitized with hot water
and non-toxic disinfectant or detergent, then thoroughly rinsed. Water bottles and food
dishes should be cleaned and disinfected daily.
BREEDING
Sex determination is the first step to breeding success. Fortunately, mice and rats are
fairly easy to sex. Neonatal male rodents can be distinguished from females by a greater
ano-genital distance. Males have one-and-a-half to two times the distance between the
anal and urogenital openings than that of females. Sexually mature male rodents exhibit
a prominent scrotum. Females can be identified by their pronounced bilateral rows of
nipples.
Sexually mature mice and rats need to be properly paired to avoid fighting and permit
successful mating. Adult male mice often fight when caged together, especially in the
presence of females. Therefore, a single male mouse should be housed with one or more
mature females. Rats, on the other hand, can usually be caged in groups of males and
females without the aggression problems.
Female mice become sexually mature at about 50 days of age. They have an estrous
(heat) cycle of roughly every 4 to 5 days throughout the year, unless bred. Female mice
are usually receptive to males for 12 hours of this cycle, most frequently at night. They
also have a fertile postpartum estrus, which means that they can be bred within 24 hours
after giving birth.
Gestation in mice lasts approximately three weeks, but may be up to ten days longer if
the pregnant female is already nursing a litter. Litter size averages from 10 to 12 young.
Small litter size is common for a female’s first litter or in older females. New litters
should not be disturbed for the first few days. This minimizes injury or abandonment by
the mother to the young. Baby mice are weaned at about three weeks of age.
Female rats become sexually mature at about 65 days of age. They have an estrous cycle
of roughly every 4 to 5 days throughout the year. Breeding usually occurs at night during
the 12 hour period of receptiveness to the male. They also have a fertile postpartum
estrus, and can be bred within 48 hours after giving birth. However, unlike mice, this
usually does not occur because the male should not be allowed to remain with the female.
If he is not removed, he may cause injury to the pups.
Pregnancy lasts about three weeks in rats. Litter size averages 6 to 12 young, but smaller
litters are common as was described for mice. The female and her litter should not be
disturbed for the fist few days after birth, because a stressed female rat may injure or
destroy her pups. Rats are weaned at about three weeks of age. The female will resume
her normal estrous cycle within 2 to 5 days after the young are weaned.
MOUSE AND RAT FACTS
Mouse
Rat
Life span ...................................................................... 1.5-3 years ........................... 2.5-3.5 years
Cage temperature range ............................................... 65-80 degrees F.................... 65-80 degrees F
Relative humidity range .............................................. 40-70%................................. 40-70%
Breeding age ................................................................ 50 days (male)...................... 65-110 days
50-60 days (female)
Estrous cycle................................................................ 4-5 days................................ 4-5 days
Gestation period .......................................................... 19-21 days............................ 21-23 days
Litter size ..................................................................... 10-12 young ......................... 6-12 young
Weaning age ................................................................ 12-28 days............................ 21 days
Common Medical Conditions:
Chronic Murine Pneumonia (Murine Mycoplasmosis)
Common signs: Sneezing, labored breathing, red tears and nasal discharge, anorexia, lethargy
Tyzzer’s Disease
Common signs: (usually young mice) ruffled fur, lethargy, hunched posture, poor appetite, occasionally
diarrhea
Sendai Virus
Common signs: (usually in nursing mice)- include labored breathing, chattering, rough hair coat, weight
loss, and death.
Sialoacryodenitis
Common signs: (usually young rats)- squinting, blinking, and rubbing @ eyes. Sneezing and swelling may
occur later as well as swellings below or around the eyes, production of red-brown tears, and self trauma to
the eyes from rubbing. Other respiratory signs may be present
Tumors
Common signs: a swelling behind the front legs, along the sides and flanks, and along the underside of the
body.
Red-Brown Tears of Rats
Common signs: (usually rats)- red tears or nasal discharge
Ring Tail
Common Signs: (usually young rats)- tissue death, and sloughing of the tail
Overgrown Incisors
Common signs: A change in the normal ratio of incisor tooth size of 3:1 (lower to upper)