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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
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 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 Barbering - moderate Bite wounds
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-Isolator TM 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 Cunliffe-Beamer, Terrie L. The Laboratory Mouse. CRC Press, Boca Raton, FL Harkness, J.E. and J.E. Wagner. The Biology and Medicine of Rabbits and Rodents. Williams and Wilkins Hrapkiewicz, Karen, Leticia Medina, and Donald D. Holmes. Clinical Laboratory Animal Medicine: An Introduction, 2nd Ed. Iowa State University Press, Ames, IA Laber-Laird, K., M.M. Swindle, and P. Flecknell, Handbook of Rodent and Rabbit Medicine. Pergamon Press, Oxford, UK