Animal husbandry is the applied science of providing an optimal environment for a population of animals. The practice of mouse husbandry encompasses all of the activities necessary to produce mice of high quality, including care and feeding, cleaning of the equipment and physical surroundings, and constant concern for the health of each animal. The implementation of good mouse husbandry begins with the design and construction of the physical facilities and continues through maintenance of an environment conducive to good health, growth, reproduction, and survival of the animals.
FACILITIES FOR MICE
The design and construction of a mouse room should meet certain standards regardless of the type of research carried on or the use of the room solely for breeding or maintenance. If mice are produced internally (not procured from an outside source) the breeding rooms should be separated from rooms in which experimental procedures are carried out. If mice are procured from an outside source, they should be quarantined at least 2 weeks in a room remote from the research area. The isolation of such areas may be accomplished in separate buildings, on different floors of the same building, or perhaps only at opposite ends of the same floor. The objective is to minimize the transfer of diseases between the groups of animals. In addition to the racks and aisle space, there must be a space for temporary storage, a work table, a sink (possibly outside of the room), and waste receptacles.
Mouse rooms should have two doors, one opening from a clean supply corridor and the other into an evacuation corridor. The appearance and degree of contamination of the evacuation corridor should not differ appreciably from the clean supply corridor. In a research situation there must be access from the mouse rooms to laboratories. To incorporate the supply-and-evacuation corridor concept into a workable relationship with laboratory rooms, it is necessary to compromise the traffic pattern to permit the people from the laboratory to cross one of the two corridors.
The decision about which of the corridors adjacent to the mouse rooms will function as the clean supply corridor can be made on the basis of the amount of contamination present in the colony. If disease incidence is low, the evacuation corridor can be adjacent to the laboratories; if disease incidence is high or if the experimental procedure involves communicable disease vectors, the supply corridors should be adjacent to the laboratories.
Materials and methods used in the construction of mouse rooms should not only conform to local building codes, but should meet or exceed the recommendations of the Institute of Laboratory Animal Resources ( 1962).
Other sources of information on laboratory animal facilities and mouse husbandry include Public Health Service ( 1963), Hill ( 1963), Hoag and Les ( 1963), and Lane-Petter ( 1963).
Racks and shelving
Racks for cages may be either mobile of fixed. Fixed racks can be attached to the floor, the walls, or the ceiling. Regardless of the system used, provision must be made for cleaning beneath and behind the racks. The bottom shelf of a rack should be no less than 6 in. off the floor; the top shelf no higher than the reach of a person of average height. The use of stepladders should be avoided.
The spacing between shelves should allow ample room for insertion and removal of cages, i.e., about 2 in. greater than the over-all height of a cage unit with the water bottle attached.
Shelves may be made of metal pipe or rods, or they may be solid sheet metal like book shelves. The supposed advantage of pipe racks is that the open construction allows greater circulation of air around the cages; however, and undesirable feature is that materials (feces, food, bedding) thrown out of the cages by mice can fall from an upper cage into one on the lower shelf. A combination of solid shelves with open structure in the back wall of the rack (or no back wall in the rack) would probably be most desirable.
Regardless of the design, the racks should be constructed with a minimum of crevices or joints where dirt might accumulate. For this reason, materials such as expanded metal, perforated metal, or structural members with many holes for adjusting shelf height should be avoided. Unless the racks are stainless steel or galvanized metal, they should be painted with coating that prevents corrosion and withstands the action of detergents and disinfectants.
Materials for construction of cages include galvanized and stainless steel, plastic, wood, glass, and paper. The most common type of mouse cage for a breeding pair is a box approximately 12 x 6 x 6 in. deep. Cages are available commercially with many dimensional variations of this basic design. Among the desirable features of cage design are the following:
If transparency is a requisite, the cage must be plastic or glass. If transparency is not a necessity, metal or opaque or translucent plastic may be used. Of the metal cages the stainless steel are by far the most durable; next in order are aluminum and stainless steel. Plastic cages include polyethylene, polypropylene, polystyrene, polycarbonate, cellulose-acetate butyrate, acrylic resin (Lucite), acrylate and metacrylate resin (Plexiglass), and melamine-formaldehyde filled with glass fibers. polycarbonate is probably the nearest to an ideal plastic for cages. It is transparent, autoclavable, and virtually indestructible.
For research institutions where small numbers of mice are to be kept it might be desirable to use disposable cages, thereby avoiding the expense of facilities for washing them. Several types of disposable plastic cages are available, including a semirigid form requiring a supporting frame and a rigid (but rather brittle) self-supporting type.
Covers for mouse cages are usually made of metal, either of punched sheets, hardware cloth, rods, or expanding metal. The material can be stainless steel, aluminum, or metal that has been galvanized, tinned, zinc plated, or aluminized. Covers can be designed to stack; however, this is not essential since the cover will generally be in use rather than in storage. The cover can either overlap the cage or be recessed within it. If the cage is made of plastic or wood, the cover should be recessed to prevent the mice from nibbling the rim of the cage. If the cage is metal, the cover may overlap the sides of the cage although this presents some disadvantages. Mice often push fecal matter or bedding material out through the cover, and recessed covers then to minimize the consequences of this activity. If hardware cloth is used for cover material, the mesh should be no larger than three spaces to the inch. Smaller mesh is more difficult to clean; larger mesh allows mice to escape. Covers should have a tag-holder attachment and some provision for lifting the cover from the cage. The cover should have a support for the water bottle and a hole in the mesh to accommodate the water drinking tube. Cage manufacturers can usually supply appropriate covers.
The food hopper can be incorporated into the cover or attached to the cage separately. A slotted hopper or one of hardware cloth having a mesh of three spaces to the inch is preferred. A hopper which is an integral part of the cover should be so constructed that mice cannot cling to it and soil the food with urine and feces. The design of the hopper should permit the caretaker to add food without removing the cage from the shelf. It should be possible to position a water bottle without moving the cage. The hopper should extend low enough into the cage to permit small or young mice to feed, but should be high enough so that large or adult mice do not have to lie on their backs to feed. The hopper must be sufficiently large to avoid bridging of the food inside. Hoppers may be covered to prevent dust from getting onto the food and to prevent contamination by stray mice.
Water may best be supplied from bottles resting on top of the cages. Each bottle is fitted with a rubber stopper and a tube of stainless steel. The tube must be constricted at the end so that the water does not flow out unless the mouse licks the end of the spout. The diameter of the tube should be ¼ to 3/8 in. A large-mouthed bottle, such as a 1-pint milk bottle, facilitates cleaning. Other types and sizes of bottles can also be used; e.g. syrup bottles, 1-pint prescription bottles, and almost any other type which can be fitted with a stopper and tube. The position of the water bottle on the cage depends on the type of cover. If the water bottle rests on top of the cover, the tube must be bent at an angle of about 105° so that the water will drain from the bottle and the tube will extend in a vertical position into the cage. The tip of the tube should reach a point about 2 in. above the floor of the cage; i.e., low enough to permit small mice to reach it and yet high enough so that the bedding material cannot be piled up to the pint of touching the tube. If the cover of the cage is designed with a bottle receptacle depressed into the cage cover, a straight tube may be used. The opening on the end of the tube should be free of burrs and sharp edges. Aluminum tubes are too soft for this purpose; mice can nibble and distort the size of the opening. When ordering bottles it is essential to specify the inside diameter of the neck of the bottle, since this is the dimension which must be fitted with the proper size of stopper. Half-pint and 1-pint milk bottles will usually take a No. 6½ rubber stopper. The cage cover should be so designed that the rubber stopper is not touching the surface of the cover. This can be accomplished by providing a metal disc on the cover against which the rubber stopper will rest. If the bottle rests on top of the cage and a bent tube is used, this is not necessary.
Water may also be provided from a central system without the use of bottles by extending pipes or tubes from a central reservoir into each cage. At the end of each of the tubes a small valve allows water to run when the mouse touches the valve stem. The tube from the central reservoir may enter the cage either through the cover or through a hole in the end of the cage.
A second widely used system of caging mice is the suspended cage. Each cage consists of hardware cloth bottom and sides which are either solid sheet metal or hardware cloth. Cages of this type are not usually used for breeding mice. Suspended cages usually have no tops. They slide into a rack on metal guides and require a pan underneath to catch droppings and urine. The pans can be lined with paper which is easily changed or they may be filled with various kinds of absorbent litter. Water bottles similar to those mentioned above may be used on this type of cage, although the method of attaching the bottle to the cage is different. The bottle is held in a vertical position on the cage by a loop of wire or a metal bracket. A bent glass or steel tube protrudes into the cage so that the tip of the tube is about 2 in. from the floor. Feed hoppers for this type of cage consist of a small chute attached to the outside of the cage. Feed placed in the chute slides down against the wire front of the cage through which the mice are able to nibble the pellets. Suspended cages of this type are usually attached to the shelves of mobile racks.
Bedding and nesting material
Bedding material serves three purposes: to provide material from which the mice can make nests, to absorb the fecal and urine wastes, and to provide insulation. Among the materials in common use are pine, cedar, or other wood shavings, sawdust, ground-up corn cobs, shredded flax, chopped straw, hay, absorbent clay such as fuller's earth, shredded paper, and blotter paper in the form of sheets. Regardless of the type of material used, several prerequisites must be met. The material should be clean, dry, and free of extraneous objects and waste matter. It should be metabolically neutral, since mice will nibble the bedding regardless of its composition. The bedding should be about ¾ in. deep in the case of shavings and other fluffy material, and about ¼ in. deep for such things as fuller's earth. In any case, it should be sufficient to absorb all of the urine, wet fecal matter, and water which may drip from the water bottle. The bedding material must fall freely from the inverted cage during cleaning. Some types of bedding tend to stick to the surface of the cage. White pine shavings meet most of the criteria indicated above.
Cage tags and card holders
For record keeping and other information it is convenient to have a card holder of sheet aluminum or other thin metal attached to the cage or cover. If cages and covers are washed with equal frequency, the card holder may be attached to either the cover or the cage. However, if the cages are washed more frequently than the covers, the card holder should be attached to the cover to minimize the number of times the card has to be transferred from the dirty card holder to the clean.
Floors, walls, ceilings
The floors of the mouse room should be cleaned regularly during periods of active use, usually at the end of each day. A vacuum cleaner or a wet mop should be used to pick up pieces of shavings or other spilled material. Sweeping should be avoided; any essential sweeping should be done in a manner that will raise the least amount of dust. After the floor has been swept of vacuumed, it should be swabbed with a disinfectant containing a detergent. This disinfectant should be allowed to stay on the floor for the length of time necessary to achieve disinfection. The walls and ceilings of the mouse room should be cleaned and disinfected as frequently as is necessary. This can be determined on the basis of bacteriological sampling or visual observation.
Fixtures and equipment
Light fixture and any flat surface which accumulates dust should be cleaned with a vacuum cleaner and swabbed with disinfectant. Cage racks should be similarly cleaned at least once a week, preferably when they are empty. Sinks should be disinfected at least once a week. Tables and carts used as work surfaces should be disinfected after each use. In installations where walk-in washers are available, tables and carts may be removed from the mouse room and put through the washing machine.
Forceps and ear punches
Forceps used for handling mice should be disinfected between successive cages. For this purpose it is convenient to have two containers of about ½-pint liquid capacity, each about three-quarters full so the forceps are immersed about 3 or 4 in. Ear punches should also be disinfected between successive cages. The disinfectant should be of a type which acts quickly but is not harmful to the mice, e.g., bound iodine or alcohol.
Mouse rooms equipped with sinks should have dispensers for disinfectant hand soap. Caretakers should wash their hands upon entering and before leaving a mouse room. For general cleaning purposes solutions containing phenyl derivatives, bound iodine, or quaternary ammonium compounds can be used. Sodium hypochlorite or bound iodine solutions in low concentrations can be used for disinfecting items which may come in contact with mice. Phenolic and quaternary ammonium type compounds should not be used to disinfect items which come in contact with mice, since either or both might be carcinogenic or cause skin irritations.
Dirty cages should be taken from the mouse room for disposal of the soiled bedding. Dirty cages may be stored temporarily in the wash area, but in no case should they be allowed to remain uncleaned beyond the end of the working day. Soiled bedding accumulated in the wash area should be incinerated or disposed of in such a way to render it incapable of contaminating animal areas or people who come in contact with it. The waste bedding material may be removed simply by inverting the cage or by use of a vacuum hose. After the waste material has been removed, anything clinging to the cage surface should be scraped off with a rubber-tipped scraper.
In small animal colonies cages can be washed by hand in a sink with a washing and rinsing basin. Cages should not be hand dried; they should be allowed to dry in air in a clean area. Rinsing the cages in hot water will hasten the drying.
Various types of machines are available for washing cages. The so-called batch washer is designed so that a number of cages may be stacked in the machine and washed as a group. The cages must be stacked so that the spray jet will reach all surfaces. Another type is the tunnel washer. This is a long tunnel-shaped device through which the cages pass on a conveyer belt over jets of hot water. A tunnel washer is easily adapted to a supply-evacuation corridor and barrier system. Cages enter the machine in the evacuation area and emerge into the supply area, having passed through a wall. In mouse colonies where extreme cleanliness is required cages may be sterilized after they are washed. The autoclave should be built as a pass-through device so that the clean, sterilized cages can be removed from the chamber in the supply area.
In a small mouse colony bottles may be washed with a hand brush. For a large operation various kinds of bottle-washing machines are available. Some of these are of the soak type, others use a system of spray jets. Where machinery can be used, it is desirable to wash the bottles in their handling cases. One type of machine handles bottles under the batch system; that is, a case or more (up to three cases of bottles) may be placed in the machine and be washed and removed from the clean side. In a tunnel-type bottle washer the inverted cases of bottles are placed on a conveyer belt and passed over a series of spray jets for washing, rinsing, and sterilizing, or rinsing with a chemical disinfectant. Bottles may be sterilized in an autoclave and passed into a clean area through a double-door system. If the bottles have been autoclaved, they should not be filled with cold water as this will cause breakage; they should be allowed to cool to 100°F or to room temperature before cold water is added.
Bottles may be filled with water either automatically by a device integral with the washing machine or they may be filled by means of a multiple-jet filling header, the number of filler jets being equal to the number of bottles per case.
Stoppers should be washed at the same time as the bottles, but in a different machine. The stoppers may be placed in washing water in a wire basket and the water brought to a boil in a steam-heated sink. They may also be rinsed in a wash solution and then sterilized in an autoclave as indicated above for the cages and bottles. If the stoppers are to be inserted in the bottles by hand, they should be immersed in a disinfectant solution just prior to being handled. This will insure that the stoppers will remain clean until they reach the mouse room. Dirty stoppers should be rinsed with a strong jet spray to remove the bits of shavings and other materials clinging to them.
Other equipment used in mouse rooms must be sanitized either in the room by means of swabbing with a disinfectant or in a separate wash area. The equipment should be passed through a suitable washing machine or swabbed with washing compound and passed through a chemical dip from the evacuation area to the supply area. Unwashable materials and equipment used in the mouse room should be of a disposable type.
MOUSE ROOM EQUIPMENT
Tables, carts, dollies
Two kinds of operations are usually carried on in a mouse room: maintenance and research. For either operation it is convenient to have a tablemounted on casters. The surface of the table should be smooth and preferably made of stainless steel or galvanized iron. One or more shelves may be fitted beneath the surface. The size of the working table depends on the aisle width and on the size of the cages being used. The width of a table should be at least twice the width of the cages being used, and the length of the table should be approximately three times the length of the cages. It is best to allow a little leeway in both directions. Tables can be obtained which are adjustable in height although the standing-height work surface of 35 in. is usually used. The table may have four swivel casters or two swivel and two rigid casters. In either case the diameter of the caster should be no less than 4 in. The larger the caster the easier it is to move the table. If the mouse room floors are not level, the table should be provided with locking type caster. Although metal or hard fiber wheels roll most easily on a smooth floor, rubber-tired wheels are easier to roll over small obstructions.
If mice must be removed from the mouse room, it is best to have a cart with several shelves that will hold 10 or 20 cages. Since this type of cart will be moved over doorsills and through corridors, it is desirable to have casters with fairly large (6 to 8 in.) rubber-tired wheels.
Cages, covers, water bottles, feed, and various types of containers can be moved most conveniently on dollies designed specifically for the load. The dolly may be made of angle iron with the inside of the angle upward and mounted on rubber-tired casters. Cages can be stacked directly on the dolly; covers and water bottles must be held in trays or cases stacked on the dolly.
Containers for feed, bedding, or other material used in a mouse room should be covered and kept off the floor. Since all containers must be cleaned frequently, they must be constructed of noncorroding metal or plastic that will withstand high temperatures. If the containers are to be moved, they should be placed on dollies mounted on casters. For dispensing food, it is convenient to have a covered hopper mounted above the work table with an opening at the bottom from which the food may be picked up with a scoop. The advantages of this type of hopper are: (1) Food may be added to the top and removed from the bottom, so that the older food is used first; (2) it prevents the accumulation of ground particles of food; and (3) contamination of food is minimized, since the hopper is located above the work surface.
Devices for killing mice humanely
Every mouse room should be equipped with a device for killing mice humanely. A simple device is a covered can or jar of about 5-quart capacity lined with a plastic bag. If mice are to be killed in the mouse room, ether or chloroform should not be used; instead, carbon dioxide from a small cylinder fastened under the work table or located at some central point in the room may be used. When enough mice have been accumulated in the jar to cover the bottom, a tube from the gas cylinder is inserted and enough gas is released into the jar to kill the mice.
If the mice can be taken out of the room to be killed, chloroform may be used. In this case the animals may be accumulated in a large cage for transporting them. Chloroform as liquid should not be allowed to come in direct contact with the mice. A wad of cotton or paper towel can be moistened with the liquid and placed in the bottom of the jar beneath a piece of paper or plastic sheet. Regardless of the method used the number of mice should not exceed that which would cover the bottom of the container. Mice should never be accumulated to the extent that they suffocate or trample each other before they are killed. After the mice are killed, the plastic bag should be tied with a tight knot and discarded in a container designated for that purpose. Dead mice should be removed from the mouse room and incinerated before the end of each working day. Dead mice accumulated over weekends and holidays should be placed in plastic bags and stored in a freezer until they can be taken to the incinerator.
There are usually only two situations in which mice must be handled: during the changing of cages and during experimental procedures. Regardless of circumstances under which the mice are handled, the mice should be touched with the hands as little as possible. At the time of cage changing the mice should be transferred from the dirty cage to the clean cage with a pair of long forceps. The mice may be picked up either by the tail a short distance from its base or by the loose skin at the back of the neck. In either case the forceps should be used so that the mouse is not pinched, although held firmly enough so that it cannot break loose from the grip. With practice the caretaker should be able to pick up the mice deftly with a minimum of pursuit in order to avoid undue stress to the mice. The mouse should be lowered into the clean cage to the point where its feet are touching the bedding material. Mice should not be dropped but placed in the cage. Pregnant female mice should be handled with extreme care. In rare instances a female will be found giving birth to a litter at the time the cages are being changed; it is advisable to leave this cage unchanged but marked for changing at a later time. Disturbing the female at this time might cause her to destroy the litter or result in abnormal delivery of those not yet born. Newborn or very young mice may also be handled with the forceps although extreme caution must be used to avoid injury due to squeezing. Very young mice should be placed in a cluster preferably touching each other when they are placed in a clean cage. If the newborn mice are scattered when they are placed in the clean cage, it may be some time before the female has recovered from the stress of being changed and gets around to picking them all up. If they are placed in a cluster, she will be more likely to attend to them sooner. Sick mice found in a breeding colony should be removed from the mouse room and either killed or sent to a diagnostic laboratory.
Under certain circumstances it is necessary to pick up the mice by hand, for example, if the ears are to be notched or the toes clipped for identification. Toe clipping should be done only when it is necessary to identify young mice whose ears have not yet grown to an extent where the ear punch can be used. In special cases it might be necessary to use a combination of ear punching and toe clipping even on adult mice.
The frequency of cage changing depends on several factors. If wood shavings or similar material is used as bedding, the cages should be changed at least once a week and in some cases twice a week. If a specially absorbent material is used, it may be possible to extend the changing period to 2 weeks or more. A balance must be struck between the degree of cleanliness desired for the mice and the stress that mice undergo every time they are changed to a new cage. If the cage covers are constructed in such a way that they do not easily become soiled, it is possible to extend the changing periods for covers to as long as 4 to 8 weeks. If the covers become soiled, they should be changed with the same frequency as the cages. The principal reason for less frequent changing of covers is to avoid wasting usable food.
Young mice may be weaned any time after they are 18 days of age. The actual age chosen will depend on the strain of mice being maintained. Some mice mature more rapidly than others. It is essential that the litter be removed from the parents before the young mice become sexually mature. This is usually at 4 to 5 weeks of age. In some cases it is necessary to wean a litter earlier than anticipated because of the presence of a second litter. If mice are to be held for any period of time after weaning, males and females should be kept in separate cages. All mice should be carefully examined at the time of weaning and those not conforming to the desired quality should be culled.
Feed and feeding
Mouse food is commercially available in the form of pellets. Some manufacturers can supply several varieties for specific purposes, e.g., a special formulation for breeding mice, pasteurized feed for mice maintained under pathogen-free conditions, sterilized diets for germ-free mice, diets fortified with extra amounts of heat-labile vitamins (for installations where the feed is autoclaved before it is brought into a mouse room), and diets with specified levels of fat or protein ( Chapter 5). The standard formulations are usually sufficient for general use; however, it is advisable to investigate the formulation of the diet, the ingredients, the chemical analysis, methods of shipping, and whether the diet is free of potentially pathogenic organisms. Feed should not be stored for more than 30 days from the date of milling. In warm, humid climates storage time must be even shorter unless air-conditioned or refrigerated storage facilities are available.
New food can be added to hoppers either at the time of cage changing or as a separate operation. Feed should not be touched with hands; a small metal scoop is much more sanitary and is actually more convenient and efficient to use. Old feed, that is, feed not used up by mice in a cage that is being terminated, should never be reused; it should be discarded and incinerated along with other waste materials from the mouse room.
When cages are being changed it is more practical to change in a vertical sequence; that is, columns of cages, rather than rows, are changed successively. The vertical sequence system requires less moving of the work table.
Cages containing mice should be handled with a smooth, even motion to minimize disturbance of the animals. Whether empty or occupied the cages should be picked up and set down with a minimum of noise. Careful handling will not only reduce the level of noise in the room, it will also extend the useful life of the cage.
Bottles may be removed from the cages as each cage is about to be changed or they may be removed by sections, that is, about 50 bottles in a group. When clean bottles are installed on cages each bottle should be checked to ascertain that the stopper is firmly fastened and that the water has entered the water-delivery tube. The latter can be accomplished by holding the bottle downward and shaking it gently until air bubbles come out of the tube indicating that the tube has been filled with water. Clean water should be provided at least twice a week. Under certain special circumstances two or three changes per week may be necessary. Bottles should not be refilled, since any contamination accumulated in the bottle will be retained.
ENTRY AND EGRESS
Systems of entry into animal quarters depend on the degree of cleanliness to be maintained. In so-called conventional animal colonies, the only requirement is that personnel should wear garments which are worn only in the animal area, such as laboratory gowns or coveralls, and shoes which are worn only in the animal areas. Clothes should be changed outside of the animal room in a location accessible from the outside and also from the animal rooms. Personal belongings should be kept out of the mouse room, since these items usually cannot be sanitized in any way before entering. Food for human consumption should not be brought into the animal quarters.
All mice brought to an established animal colony should be quarantined for a period of 2 to 4 weeks prior to entry. If possible, castrated mice from the established colony should be exposed to the quarantined mice to ascertain whether a transmissible disease might be carried by the new arrivals. Various bacteriological tests should also be carried out. The mice should be examined for ectoparasites and small numbers should be killed and examined for endoparasites.
When mice are transferred from one room to another within the same building, transfer should be made in small disposable paper or plastic containers or in freshly changed cages. Dirty cages should never be moved from one mouse room to another. Mice to be shipped from the animal colony to an outside destination should be removed from the animal room and assembled in a special holding or shipping room. Preparations for shipment should not be carried out in the breeding rooms.
Feed for a conventional colony of mice should be delivered to a room accessible both from outside the building and from the animal room. Feed should be stored in a dry room at low temperatures and should not be kept longer than 30 days from milling before it is fed to the mice. Feed manufacturers can stamp the milling date on each bag. Conventional (not pasteurized) feed is usually delivered in paper sacks. The outside of these bags can be disinfected with a sponge when the bags are brought to the animal rooms. It is also possible to have the feed delivered in double wrappers in a manner such that the outside wrapper is removed as the bag of feed is delivered to the storeroom. Thus any contamination accumulated during shipment will be left outside of the storage area.
Bedding for conventional colonies is usually safe enough to use as it comes from the vendor provided it has been checked to ascertain that the material is clean and free from obvious contamination. However, it is preferable to sterilize or at least pasteurize the bedding when it is being introduced into the animal quarters. Material such as wood shavings, ground corn cobs, shredded flax, etc., can easily be sterilized or pasteurized. Bedding should never be sterilized with ethylene oxide gas. Such a procedure results in the accumulation of ethylene glycol as a result of the reaction of ethylene oxide with the moisture in the bedding. The glycols are harmful to certain strains of mice and may cause hemorrhagic disease ( Chapter 18).
Mice should be closely observed for signs of disease or evidence of incapacity of any type at the time cages are being changed. More frequent observations may be necessary in certain types of experimental procedures, although it must be remembered that cages should not be disturbed so frequently that the mice will become unduly stressed. Gross observation is not sufficient to detect all types of disease so it is advisable to remove representative mice periodically for autopsy by a pathologist. if mice cannot be killed for autopsy, it is possible to detect some diseases by fecal examination. Mice should be placed in a beaker or some type of disposable container; after the fecal pellets have been accumulated, the containers should be covered and sent to a diagnostic laboratory for analysis. Detailed records should be kept of the mice sampled so that if some undesirable condition is detected, the mice can be removed from the colony or medication can be applied.
Unless precluded by the protocol of the experiment, sick animals should be removed from the colony whenever they are observed. In a breeding colony maintained for perpetuation of a strain the culling can begin with newborn mice; those smaller than normal should be removed from the litter. At any time prior to weaning, mice obviously behind their littermates in growth or apparently ungroomed should also be removed. The most severe culling should be practiced at the time mice are weaned. It may be advisable to weigh the mice at weaning to determine whether they conform to the expectation for that strain. With experience it is possible to detect mice that are underweight by observation. In a breeding colony selection of breeders for the next generation is of utmost importance. The criteria for selection of breeders can be determined only on the basis of experience, although certain signs are indicative of good quality. The mice should have glossy coats, they should be active and vigorous, they should not be under- or overweight, and they should not have any injury that might have been sustained between birth and weaning.
Implementation of good mouse husbandry includes design and construction of facilities and provision of cages and other equipment for proper care of the mice. Sanitation of facilities and equipment is of utmost importance; clean cages, bedding, and water bottles must be provided on a regular schedule; mice, feed, water, and mouse room equipment should be handled in a manner that results in clean, efficient operation with minimum disturbance of the mice. Entry and egress of personnel, mice, equipment, feed, bedding, and waste must be accomplished so as to minimize the possibility of introducing disease organisms or vectors of disease. Constant vigilance, supplemented with good diagnostic services, must be exercised to promote the health and phenotypic quality of the mice.
1The writing of this chapter was supported in part by Public Health Service Research Grant GM 10236 from the National Institute of General Medical Sciences.
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