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The genus and species of the laboratory mouse is mus
musculus and is of the order Rodentia. The
laboratory mouse has been domesticated by man for many generations
and is in general a very docile and easily handled animal. Other
notable biological characteristics are their very acute hearing,
well developed sense of smell, poor vision, small size and short
generation interval. Mice are by far the most common laboratory
animal used for research.
There are two common methods by which to characterize
laboratory rodents; genetics and microbial flora. Common genetic
categories are "random-bred" which are managed to maintain genetic
diversity by mating unrelated animals; "Inbred" rodents which
are managed to maintain genetic homozygosity by breeding siblings;
"F1 hybrid rodent" in which two inbred strains are crossbred
for one generation; "transgenic" in which specific genetic
material has been introduced into the genome of another inbred
rodent strain; "mutant" rodents which are inbred with developed
genetic mutations. The microbial flora of rodents are used for grouping:
Specific Pathogen Free rodents (SPF) are free from
known bacterial, viral, and parasitic mouse pathogens, as opposed
to "conventional" mice, which are not known to be free of
pathogens. Other less common microbial groups are axenic, which
are free from all microbial organisms, and gnotobiotic, which have a known microbial flora.
Inbred, outbred, hybrid, transgenic or mutant rodents are
available from many commercial sources. Vivarium
personnel are familiar with many of the commonly available strains
and will assist in locating animals available for purchase.
To order
animals the investigator must provide the UC Riverside Animal Use
Protocol number.
The laboratory mouse is a docile animal and is easily
handled. Animals grouped soon after weaning usually coexist
peacefully. However, some strains of mice (i.e. BALB/cJ, SJL/J,
HRS/J) will begin to fight even if grouped at weaning. Breeding
males that have been removed from breeding cages and caged
together will usually fight. Wounds on the tail and hair loss
(barbering) are good signs of
aggression between cagemates.
Mice, like most species have a circadian rhythm. Investigators
should be aware that this may affect biological data and should
standardize the time of day that samples/measurements are taken to
avoid this affect. The standard light/dark cycle is 12/12. This light cycle can be modified upon the
request of the investigator in special circumstances.
The adult mouse weighs approximately 40 grams and this small
size and resulting large surface area/body weight ratio makes them
susceptible to changes in environmental conditions. The core body
temperature is easily affected by small changes in temperature
which may modify the physiologic responses of the animal.
17 The acute hearing
of mice makes them highly sensitive to ultrasounds and high
pitched noises inducing a stress response that has been
empirically related to cannibalism of pups by their dams. The well
developed sense of smell is used to detect pheromones used in
social interactions. The poor vision of mice makes them unable to
detect color and red light is often used to observe animals during
the dark cycle.
| Adult body weight: male |
20-40gm5 |
| Adult body weight: female |
20-40gm5 |
| Body surface area |
10.5(wt. in grams)2/35 |
| Life Span |
1.5-3 years5 |
| Food consumption |
15 gm/100 gm/day5 |
| Water consumption |
15 ml/100 gm/day5 |
| Breeding onset:male |
50 days5 |
| Breeding onset:female |
50-60 days5 |
| Gestation Period |
19-21 day,5,24 |
| Body Temperature |
36-37C21 |
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36.5-38.0C5 |
| Heart rate |
500-600 beats per minute21 |
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325-780 beats per minute5 |
| Respiratory Rate |
84-230 per minute21 |
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60-220 per minute5 |
Most mice are housed in shoebox cages composed of polypropylene
(opaque) or polycarbonate material (clear) with a wire bar lid used to hold the water bottle and feed
(figure1).
Bedding is placed directly into the shoe box cage allowing the
absorption of urine and the animal to burrow and/or den. This type
of cage will hold 4-5 adult mice depending on the size of the
cage. When removing the lid from this type of cage it is important
to remove the water bottle to prevent spillage. If the cage is to
be transported the bottle should be turned sipper tube up to prevent spillage during transport
(figure 1). However, you should remember to
turn the bottle back over to allow access to water after
transport. The caretaking staff, change the cages twice per week,
thereby providing the animal a clean cage with new bedding, food
and water. Water bottles and feed hoppers are checked daily by
caretakers to insure the provision of water. Some mice are housed
on wire mesh bottom cages to allow collection of feces and urine
or to prevent contact with bedding. This type of housing is not
preferred and is used only when dictated by experimental design.
Suspended cages are occasionally provided with automatic watering
which is supplied by a nipple valve (i.e. lixit) located in the
back of the cage that is operated by animal contact. When
replacing a suspended cage that is provided with automatic
watering it is important to push the cage fully into the rack care
to insure that the lixit fully extends into the cage, allowing the
animal access to water. Occasionally a mouse will jam the lixit
open resulting in a constant dripping of water from the lixit,
saturating the bedding material. Upon observation the bedding will
appear much darker. This problem should be reported to husbandry
personnel immediately to allow correction.
Pelleted natural ingredient diets are used to feed all rodents
and are composed primarily of cereal grains which are supplemented
with additional protein, vitamins and mineral. Due to the nature
of this type of diet the exact composition can vary substantially
from lot to lot. The water provided to animals is chlorinated tap
water.
Some mice are housed to prevent the acquisition of rodent
pathogens. Rodent pathogens often do not produce clinical signs in
affected animals but often have an immunomodulating effect.
Therefore, this type of housing is important for studies that
involve the immune system. Immunocomprimised animals, which are
sensitive to opportunistic agents, are also housed in this fashion
to allow for their long term survival. These animals are housed in
sterilized cages and are provided sterile food and water. Access
to this housing area is limited to prevent inadvertent fomite
transmission of rodent pathogens by personnel.
Mouse colonies tend to be very labor intensive and are
discouraged for the production of commercially available strains
of mice. The cost of breeding mice for research use far outweigh
the cost of purchasing from commercial vendors. Also, it is very
difficult to maintain the genetic heterozygosity required for
outbred mice in small colonies and to prevent subline divergence
when breeding inbred mice. For strains not available commercially
or in instances where neonatal or fetal animals are required,
breeding colonies are maintained. Investigators requiring the
establishment of breeding colonies should consult with the Animal
Care Unit to assure proper management of the colonies. Breeding
animals have different nutritional requirements, which if not
provided, will have a detrimental effect on reproductive
performance. Light cycles are important in breeding mice and are
provided with 12 hours of light and 12 hours of dark. Deviations
from this cycle will effect reproductive performance.
Cage cards are utilized to identify the strain of mouse, sex,
number, principal investigator, and research protocol. Cage cards
should not be removed from the cage to avoid misidentification of
the animals. Temporary identification of individual mice can be
accomplished by pen marks on the tail, hair clipping or dyeing the
fur. Pen marks will only last 1-2 days whereas hair clipping may
last up to 14 days. Permanent identification methods can be
achieved by tail tattooing or microchip implantation. Tail and toe clipping are
not recommended. Ear punch identification can be utilized but may be
obliterated by fighting between individuals (figure
2).
When handling mice it is advisable to wear gloves to prevent
the development of allergies due to direct contact with animal
allergens. Mice are usually caught and lifted by the tail. The
tail should be grasped between its midpoint and the mouse's body
(picture). The tail may be grasped with the thumb and forefinger
or by the used of smooth-tipped forceps. With this simple method
of holding, they may be transferred to another cage, a balance,
identified, examined casually or sex may be determined. Pregnant
mice or very obese mice may be handled by this method but they
should be supported by use of the second hand placed under their
feet (future picture). However, such restraint is not sufficient
for treatment and close examination. For more effective control,
the mouse may be held by the tail and placed on a table or other
surface, (preferably one such as a wire cage lid that the mouse
can grasp) and the loose skin over neck and shoulders grasped with
thumb and fingers (figure 3).
It is necessary to perform this maneuver expeditiously, or the
mouse may turn and bite. Once the mouse is grasped correctly, the
head is adequately controlled. Restraint is improved if the tail
or the tail and rear legs are held by the third and little fingers
of the same hand or with the other hand (figure
4).
Mice should not be dropped into the cage, which may result in
spinal fracture, but should be lowered into the cage and released
upon contact with the bedding.
Mice less than two weeks of age can be handled by grasping the
loose skin over the neck and shoulder with thumb and forefinger or
smooth tipped forceps (figure 5).
Handling neonatal mice should be avoided especially during the
first few days after birth to avoid cannibalism or litter
abandonment. If it is necessary to handle the litter, remove the
dam to a separate cage and handle the neonates using plastic
gloves to avoid contamination with human scent. Multiparous
females are less likely to cannibalize if they have been
successful mothers and should be chosen if litter manipulation is
necessary.
Numerous types of restraint devices are commercially available
to restrain mice. Quality devices prevent the animal from turning
around yet allow easy access to the tail or legs
(figure 6).
Devices should also be easy to clean and provide adequate
ventilation. For tail vein injections a wire box cage top can be
turned over and the tail gently passed through the wire bars
preventing the mouse from turning (future picture).
Male and female mice can be differentiated
by observing the distance from the anus and genital papilla which
is greater in males (figure 7). This difference is also present in neonatal
mice.
Mice that are moved indoors can be transported in their cage
after removing the water bottle and placing it upright in the cage
lid to prevent spillage. It is recommended that a permeable drape
be placed over the cages to darken the cage and prevent over
arousal of the mice during transport. Mice cannot be transported
out of doors or by vehicles by other than husbandry personnel.
Investigators can request transfer to other buildings by
contacting the appropriate husbandry staff.
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