Biology and husbandry of the mouse

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1 Biology and husbandry of the mouse
Adapted from “The Biology and Medicine of Rabbits and Rodents”, J E Harkness and JE Wagner, eds., 3rd edition, 1989 And “Mice Biology & Husbandry”, Florida International University NDSU-IACUC

2 Origin and description
Mus musculus Research mice divided into two categories Ecologic category germfree (axenic), defined flora (gnotobiotic), specific-pathogen free, conventional mice Genetic category random-bred mice, inbred mice (at least 20 consecutive brother-sister matings), F1 hybrid (mating mice of two different inbred strains) NDSU-IACUC

3 Anatomic and physiologic characteristics
Wide variety of mutants available Spontaneous neoplasms in many inbred strains Male spleens 50% larger than female Dentition: 1/1, no canines, no premolars, 3/3 molars; no deciduous dentition; open-rooted incisors 16 total teeth, can overgrow and develop malocclusion NDSU-IACUC

4 Anatomic and physiologic characteristics
5 toes on each foot – walking pads and sweat glands that open to the foot surface No hair on nose, palms, lips and soles Poor thermoregulation Normal rectal temperature is 98.5 F A healthy new born should have 286 +/ bpm and an adult should have 632 +/ bpm. Blood pressure – 83/164 mm Hg Respirations – 163 breaths per minute NDSU-IACUC

5 Anatomic and physiologic characteristics
Highly concentrated urine – specific gravity of 1.058 Males have strongly scented, allergenic urine containing large amounts of taurine NDSU-IACUC

6 Anatomic and physiologic characteristics
3 pairs of thoracic and 2 pairs of inguinal mammary glands ventral midline, flanks, thorax, portions of neck Squamous nonglandular and glandular stomach Inguinal canals open for life in males Male has os penis NDSU-IACUC

7 Anatomic and physiologic characteristics
Lungs - single lobe on left, 4 lobes on right. Esophagus; covered by striated muscle. Old mice can develop calcification in heart. Brown fat is found adjacent to the thymus, in the axillae, along the jugular veins, near the hilus of the kidney, and beside the urethra. The most prominent masses occur between the scapulae (hibernating glands). NDSU-IACUC

8 Anatomic and physiologic characteristics
Liver weighs more in female than male. Pancreas is a diffuse structure stretching over a portion of the small intestine. The right kidney is usually larger and located further anterior than the left. The male usually has larger kidneys than the female. NDSU-IACUC

9 NDSU-IACUC

10 Anatomic and physiologic characteristics
Adrenals of female mice are larger than males. Females that develop in utero between males may be masculinized Fecundity lower in winter NDSU-IACUC

11 Anatomic and physiologic characteristics
Lee-Boot effect Female mice housed together in small groups (4-5) without a male present can cause an increase in spontaneous pseudopregnancy. Overcrowded females (30-40/cage) can become anestrus. This is caused by female odors. Can be negated by individual housing. NDSU-IACUC

12 Anatomic and physiologic characteristics
Bruce effect Pregnant mice exposed to a strange male during preimplantation period (day 1-5 post breeding) can block/abort the pregnancy. Seen most frequently in the hour post breeding period. Caused by an androgen-dependent olfactory pheromone contained in male urine. If the strange male was from the same strain, pregnancy is blocked in 30% of the females. If the strange male is from a different strain pregnancy is blocked in 80%. NDSU-IACUC

13 Anatomic and physiologic characteristics
Whitten effect If anestrus or pseudopregnant female mice are paired with a male, one half of the pairs will mate on the third night. Over 90% of the above pairs will mate within 5 days. Placing the male next to the female cage (or placing male urine in the cage) will have the same effect as placing the male in the cage. Male pheromone will accelerate puberty in females that are exposed to bedding from male cages. NDSU-IACUC

14 Sexing External genitalia of male mouse P = penis S = scrotal sac
A = anus NDSU-IACUC

15 Sexing External genitalia of female mouse U = urethral orifice
V = vaginal orifice A = anus NDSU-IACUC

16 Behavior Active day and night Loose, poorly defined social structure
Adult male mice usually fight leads to abscesses, dermatitis, septicemia, death can be avoided by castration or destroying sense of smell May bite or pinch with teeth Human allergies to dander or urine develop NDSU-IACUC

17 Behavior Live 2 to 3 years but that is somewhat strain dependent
Breed from 7 to 18 months and produce 6 to 10 litters NDSU-IACUC

18 Behavior Barbering – focal loss of hair or whiskers with no trauma – due to the establishment of hierarchy and defense of territory NDSU-IACUC

19 Restraint Lift by tail, place on a ‘toe-gripping’ surface and grasp scruff of neck Do not pull tail – it is possible to strip the skin NDSU-IACUC

20 Restraint One-handed technique for injection and bleeding procedures
NDSU-IACUC

21 Housing Metal or plastic cages with wire mesh or slotted bar tops
15 sq in floor space per adult 63 sq in floor space for female with litter Should be at least 5 in high Bedding should be nonallergenic, dust-free, inedible, absorbent, non-toxic and free of pathogens (paper, sawdust, wood shavings) NDSU-IACUC

22 Housing Odor often stronger after cleaning as males mark territory
64o to 79o F with an average of 72o F Relative humidity between 40% and 70% At least twice a week cage cleaning NDSU-IACUC

23 Housing Air flow sufficient enough to provide for the heat load released from the primary enclosure. The environment within a mouse cage is higher in general, 1-4°F and R.H. is 5-10% above room environment, and will have a greater concentration of ammonia and other substances. NDSU-IACUC

24 Housing Lights on automatic timer for cycle. 30 foot candles at the working level (1 meter above floor). Noise must be within housing areas. Continuous levels above 85 dB can have auditory and non-auditory effects (immune system deficiencies, increased adrenal weights, and decreased fertility). Excessive noise will cause a sharp drop in reproduction; cannibalism; or audiogenic seizures. NDSU-IACUC

25 Housing Cages Polysulfone Polyetherimide (PEI) Polycarbonate
Polypropylene Polystyrene NDSU-IACUC

26 Housing Size Requirements Weight Floor area/animal Height
<10 g 39 cm2 (6 in2) cm (5 in) 10-15 g 52 cm2 (8 in2) “ 16-25 g 77cm2 (12 in2) “ >25g 97cm2 (15 in2) “ Female/Litter 330 cm2 (51 in2) “ NDSU-IACUC

27 Housing Bedding provides nesting material, absorbs feces and urine, and provides insulation. Bedding should be absorbent, not readily eaten, pathogen-free, non-injurious, and comfortable. Examples: hardwood chips, softwood chips, shredded paper and corncob bedding. Bedding can influence experimental data and the type of bedding used should be described when the results of a study are published. NDSU-IACUC

28 Housing Corncob - inhibits hepatic microsomal enzymes, decreases reproductive efficiency, results in decreased ammonia formation Cellulose - decreases reproductive efficiency, results in decreased ammonia Soft wood shavings - decreases barbiturate sleep time though stimulation of hepatic microsomal enzymes Cedar - lowers seizure threshold, induces hepatic microsomal enzymes NDSU-IACUC

29 Feeding and watering Pelleted rodent diet ad libitum
Automatic waterers or sipper tubes Maintenance diet: 4 to 5% fat and 17 to 19% protein 15 g of feed and 15 ml of water per 100 g body weight per day Mice eat about 4 to 5 g of feed a day NDSU-IACUC

30 Feed and water Mice require 1.5 ml/10 g of body weight/day, and drink about 6-7 ml of water/day. Water can be: distilled, from the tap, from a reverse osmosis unit, autoclaved, Chlorinated (10-15 ppm) Acidified pH NDSU-IACUC

31 Feed and water Feed formulation can be:
Natural ingredient - diets formulated with processed whole grains and subjected to limited refinement. wheat, corn, oats, soybean meal, etc. Semipurified - only refined ingredients are used (i.e. casein, soy protein). Chemically defined - only chemically pure compounds (i.e. amino acids, vitamins, EFAs) are used. formulated with a combination of natural ingredients, pure chemicals and ingredients of varying degrees of refinement. Certified - diet which is guaranteed to have no more than a minimum level of chemohazards (i.e. estrogens, aflatoxins, heavy metals). Used in GLP studies. NDSU-IACUC

32 Feed and water Feed formulation can be:
Closed Formula Diets- are commercial diets, where the ingredient composition is not readily available. The feed formula is the property of the manufacturer marketing the diet under a trade name. Open Formula Diets- are diets where the quantitative and qualitative ingredient composition is readily available. The formula can be adjusted to meet the requirements of specific research projects. NDSU-IACUC

33 Feed and water Feed Forms include: Feed treatment include:
Pellets Semi moist Gel Liquid Powder Feed treatment include: Autoclaving alters nutrient availability and may result in antimetabolites. Vitamin A, E, thiamin, riboflavin, and pantothenic acid may be lost. Pasteurization is done at 60°C for 30 minutes Irradiation is done at 4-5 mRads. NDSU-IACUC

34 Feed and water Use food within 6 month of manufacture date (180 days for most diets; 90 days for diets with Vitamin C Most chemically defined diets have a shorter shelf life Store food at less than 70°F (22°C), and relative humidity of ~ 50% or 4°C (fridge) for purified chemically defined diets NDSU-IACUC

35 Breeding First estrus at 28 to 40 days but first bred when 50 or more days of age (20 to 30 g) Mice bred too early or after 10 weeks will have decreased fertility Sexual maturity varies with strain, season, nutrition 4 to 5 day estrous cycle, 12 hour estrous, polyestrous year around, spontaneous ovulators NDSU-IACUC

36 Breeding Vaginal plug formed at copulation contains a mixture of vesicular and coagulating gland secretions. Vaginal plug usually fills the vagina from the cervical canal to the vulva. Vaginal plug usually persists for hrs % of mice with vaginal plugs become pregnant. NDSU-IACUC

37 Breeding Fertile postpartum estrus 14 to 28 hours after parturition
Vaginal smears for timing of estrus cycle Proestrus – epithelial cells, cornified cells, leukocytes Estrus – cornified cells Late metestrus and diestrus – cornification decreases and lymphocytes increase NDSU-IACUC

38 Breeding Pregnancy – increased weight gain at day 13
Mammary development – day 14 Gestation in nonsuckling dam – 19 to 21 days Simultaneous lactation and pregnancy – delayed implantation which prolongs gestation 3 to 10 days Post lactation estrus – 2 to 4 days after removal of litter Nest builders NDSU-IACUC

39 Breeding Pseudopregnancy: Stimulation of the vagina and cervix leads to prolactin release by the anterior pituitary Prolactin stimulates progesterone release by the corpus luteum, in 13 days, the placenta takes over if fertilization occurred - otherwise there is pseudopregnancy. NDSU-IACUC

40 Breeding Newborn mice are: Hairless and blind Helpless
Bald (fully haired by 14 days of age) Weaned at 21 days of age Eat solid food at 11 days. Require maternal antibody from colostrum Lack teeth NDSU-IACUC

41 Breeding Born deaf, but can hear by 21 days.
DBA/2 mice are susceptible to audiogenic seizures. Eyes open at 14 days, Poor sight Retina is composed almost entirely of rods (poor color vision) NDSU-IACUC

42 Breeding First litter smaller with subsequent litters between 10 and 12 young Weaned at 10 to 12 g Cycling in female begins 2 to 5 days postweaning Avoid early disturbances of female and litter to minimize cannibalism, mutilation and abandonment NDSU-IACUC

43 Health Routinely screen for subclinical infections
Filter against airborne infections but watch for quality of ventilation Chlorination or acidification of water will reduce bacterial contamination Stress of handling and movement allow 48 hour period of adjustment to allow immune system to return to normal function NDSU-IACUC

44 Public health See modules on Zoonotic disease and Diseases of rats and mice Zoonotic concerns Lymphocytic choriomeningitis Salmonellosis Rabies – very rare Ringworm Tapeworm infection Allergies NDSU-IACUC