Chapter Sixteen
Mice
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Species Specific Information
 OBSERVE behavior of animals as you do your
job each day.
 Recognize NORMAL patterns of eating, sleeping,
mating and moving about the cage.
 Learn what’s normal so you can better recognize
what is ABNORMAL.
Mice
 Mus musculus
efficient breeders
inexpensive to purchase and maintain
used in research more than any other animal
produce many offspring in a short period of time
 Genetics, cancer and infectious disease studies
 Over 400 documented inbred strains of mice
 Common inbred strains include:
BALB/c - albino (white coat and pink eyes)
C3H - agouti, dark brown w/ yellow bands close to tips
C57BL/6 - black
DBA - oldest inbred strain (1909); brown
From: Biology of the Laboratory Mouse, by The Jackson Laboratory,(Dover Publications, 1968), pp.406-407
Mice Varieties
 2 strains bred together are called hybrids
 “F” indicates generation of this cross (F1 - 1st)
 Outbred = CF1, ICR, S & Swiss Webster (SW)
 Transgenics: DNA from one animal into fertilized
egg of a different animal
 Knockout: the removal or blocking of a gene
 Gene therapy: correcting defective genes
 Nude mouse: naturally-occurring genetic defect
a deficiency in its immune system.
very valuable in study of immune diseases & cancer
(Image) Nude mice - normal (back), with
tumors (front)
Nude mice - normal (back), with tumors (front)
Handling and Restraint
 Grasp by skin at the back of the neck.
suitable for brief exam purposes or cage changing
 Pups < 10 days old - cup hands around body
 Grasp skin across shoulder blades with forceps.
 When more restraint is necessary:





- Catch by base of tail.
- Grasp loose skin at back of neck close to head.
- Hold tail held between fourth & fifth fingers of hand.
- Skin grasped too far from head = mouse bites.
- Must be held firmly but gently, so it will not have
difficulty breathing.
 Plastic restraint device used for long times.
Physiological Data
Temperature: 35.8° to 37.4°C (96.6° to 99.7°F)
Heart rate: 328–780 beats per minute
Respiration: 90–220 breaths per minute
Heart and respiration too rapid to be measured by
observation, but can be measured by electronic recording
devices.
Weight: adult – 25 to 40 gm; newborn – 1.0 gm
Per day  Water: 4–7 ml, or 1.5 ml per 10 gm of body weight
 Food: 3-6 gm, or 1.5 gm per 10 gm of body weight
Feces: firm, rice-sized, dark brown
Abnormal feces are soft and discolored.
Urine: strong odor, clear & yellow
Life span: 1 to 3 years
Sexing and Breeding
 Anogenital distance > in male than in female.
 To sex newborns, compare several at a time.
 2 mating systems commonly used for mice:
monogamous pairing or harem breeding
 Females are polyestrous.
Estrus every 4 - 5 days within 24 hours post parturition.
Postpartum estrus usually = successful mating.
 Newborns pink, hairless and helpless.
Eyelids sealed & ears are not yet fully developed.
White spot on the left side of the abdomen is “milk
spot,” a good indication of healthy and nursing pups.
At 10 days of age, pups fully-furred & eyes are open.
(Image) Aging Newborn Mice
One Day Old
Two Day Old
Three Day Old
Sexing and Breeding Continued
 Often, new litter just when weaning previous one.
 Separate weanlings promptly to avoid
overcrowding.
 Other breeding data:
 Sexual maturity: 40 to 60 days
 Estrous cycle: 4–5 days; postpartum estrus
 Gestation: 19–21 days
 Litter size: 6–12
 Cannibalism: Do not disturb newborn litters for
several days to prevent possible destruction.
 Weaning: 21 days, may be longer for large litters
& some strains, e.g., transgenics
(Images) Preg. And Litters
Pregnant female (“preg”)
Newborn litter - day 1
Litter - day 7
Behavior
 Nocturnal- eating and other activities when dark
 High metabolic rate, active when awake
 Mice groom themselves almost constantly for a
glossy haircoat.
Dull haircoat, decreased activity and hunched posture
are early signs of stress or disease.
 Barbering can occur and is usually harmless.
Dominant mouse sometimes bites or chews the fur off
a more subordinate mice.
 Aggressive mice should be housed individually.
 Housing young male mice together from weaning
may help prevent fighting.
(Images) Bites
Vs. -Barbering
Barbering
severe
Barbering dominant
animal
behavior
Bite wounds
Barbering moderate
Husbandry
 Hanging wire-bottom or solid-bottom shoebox cages:
groups of five to ten animals per cage
Shoebox provides mice w/ warmth, security & nesting.
 Micro-IsolatorTM cages used for special requirements
(axenic, SPF, nude, etc.).
 Solid-bottom cages washed 1 - 3x per week.
 Cage shelving washed >1x per month.
 Wire-bottom cages washed > 1x per 2 wks.
 Wire-bottom cage liner changed regularly.
 Teeth
Incisor teeth grow continuously.
Trim carefully with scissors to temporarily correct.
(Images) Mouse Caging
Diet
 Diet = 4 to 5-gram firm pellets
helps keep their incisors worn down
 Place enough diet in cage top to last several days.
 Generally fed and watered ad libitum.
 Water provided by water bottle or an automatic
water valve.
 Nonpelleted diets are also commercially available.
Used when food intake is being measured or substances
are added for experimental purposes.
Additional Reading
Anderson, R.S. and A.T.B. Edney. Practical Animal Handling.
Pergamon Press, Oxford, UK. 1991.
Cunliffe-Beamer, Terrie L. The Laboratory Mouse. CRC
Press, Boca Raton, FL. 1998.
Harkness, J.E. and J.E. Wagner. The Biology and Medicine
of Rabbits and Rodents. Williams and Wilkins. 1995.
Hrapkiewicz, Karen, Leticia Medina, and Donald D. Holmes.
Clinical Laboratory Animal Medicine: An Introduction, 2nd
Ed. Iowa State University Press, Ames, IA. 1997.
Laber-Laird, K., M.M. Swindle, and P. Flecknell, Handbook
of Rodent and Rabbit Medicine. Pergamon Press, Oxford,
UK. 1996.