Rodent Basics–Mouse or Rat
Basic Biology - Mouse
Average Life Span
Average Adult Body Weight
Daily Feed Consumption
Daily Water Consumption
Active Period
Female Reproductive Lifespan
Male Reproductive Lifespan
Length of Pregnancy
Wean
12-36 months
Male: 20-40 gm Female: 22-35 gm
3-5 g
5-8 ml
Nocturnal
12 months
18 months
~19.5 days (19-22 days)
21 days
Handling and Restraint - Mouse
Tips
Grasp animal at base of
tail; remove animal
from cage and place on
top of wire lid.
With dominant hand,
grab mouse at base of
tail; with non-dominant
hand, grab loose skin at
base of neck (scruff).
Pick up mouse, cradling
the animal in the palm
of your hand while
anchoring the tail with
your pinky.
2nd Edition RARsm
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Pick up and handle gently.
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Use care when moving them between
cages; rodents tend to grab things.
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Place rodent on wire bars or a solid
surface. Do NOT place them on filter
tops or they may chew up the filter.
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Various one-handed methods and
devices exist; you may find other
methods work better for you.
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When scared, rodents vocalize,
struggle, or bite.
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If bitten, freeze. It’s common to shake
your hand to fling the animal away
which may injure the rodent or cause it
to bite harder.
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Wash your hands with soap and water
for at least a few minutes if a bite
broke the skin. If infectious agents or
chemicals were used in the animal, see
your PI’s protocol for further
instructions.
Published 9/30/13
Page 1
Basic Biology - Rat
Average Life Span
Average Adult Body Weight
Daily Feed Consumption
Daily Water Consumption
Active Period
Female Reproductive Lifespan
Male Reproductive Lifespan
Length of Pregnancy
Wean
26-40 months
Male: 267-500 g Female: 225-325 g
15-20 g
22-33 ml
Nocturnal
15-18 months
Indefinite
21-23 days
21 days
Handling and Restraint - Rat
Capture the rat as described for the mouse (page 1).
Tips
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Do not grab animal by the tip of the tail because the skin may pull off.
Remove animal from cage by grasping the tail 1-2 cm from the base, close to the body.
Grasp the rat around the thorax with thumb or index finger under the mandible to avoid
being bitten.
With the index and middle finger placed between its jaw and shoulders to restrain the
head, use the other hand to grasp the animal around its hindquarters for additional support.
Restraint options:
2nd Edition RARsm
Published 9/30/13
Page 2
Housing
Small Mouse Box Combinations
4 males OR 5 females
1 male + 1-3 females (NO PUPS)
2 adults + 1 litter of pups (under 21 days)
Rat Box Combinations
Any number of rats is allowed as long
as they do not weigh more than 1000
grams combined. Rats that weigh over
1000 grams combined may be housed in
pairs.
*Variances to weaning after 21 days must be pre-approved by the vet staff.
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IACUC states that RAR is in charge of ensuring appropriate animal housing at all times.
RAR will flag over-crowded cages. Researchers must separate animals in a timely
fashion. If not corrected, RAR will separate and charge a fee.
If a colony constantly has overcrowded boxes, the vet may choose to inform the
investigator that RAR will stop notifying and just separate as needed and bill accordingly.
Fighting mice will be immediately separated, and RAR will notify the group.
Sexing
Anus
Anus
Vaginal
Orifice
Penile Shaft
Males have a longer distance
between anus and urogenital
opening. Penis and testicles
may be visible.
Females have a shorter
distance between anus and
urogenital opening. You can
often see a line here where the
hair growth meets from
opposite directions.
Both sexes may have a visible papilla covering the urethral opening.
Do not confuse a papilla with a penis.
2nd Edition RARsm
Published 9/30/13
Page 3
Signs of Pain and Distress
Animals respond to and show signs of pain and distress just as people. Undetected and/or
untreated pain and distress of laboratory animals not only will have adverse and undesirable
effects to research results but is also a humane issue. Use this as a reference for evaluating pain
and distress in rodents.
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Signs of a Healthy Rodent
Eyes open
Smooth fur
Long and lean posture
All nesting material has been
manipulated and appears fluffy
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Common Clues to a Sick Rodent
Squinted eyes
Hunched posture
Ruffled fur
Nest has not been built, or is poorly built
Sick mouse on ‘life raft’
(nest has not been built)
Healthy mouse in well-built nest
Criteria for Assessing Pain and Distress in Rodents
Friendly
Aggressive
Scared
Activity
Level
Alert, active
Behavior
Ears up, tail
Exploratory
shaking/quivering,
behaviors (rearing,
almost appears to
sniffing)
be on toes
Vocalization,
timid, cowering in
cage corner
Appearance
Smooth fur, long
and lean posture,
eyes open
Hunched posture,
squinted eyes,
porphyrin staining
around eyes and
nostrils
2nd Edition RARsm
Hyperactive
Looks ready to
‘spring’
Hypoactive
Published 9/30/13
Painful
Hypoactive,
lethargic, restless,
loss of appetite
Vocalization, selfmutilation,
depressed, may
not resist handling
Hunched posture,
ruffled fur,
squinted eyes,
porphyrin staining
around eyes and
nostrils
Page 4