HUSBANDRY, EQUIPMENT, AND PROCUREMENT OF MICE 541 



radiation, agents of infectious disease, and other factors of potential hazard to the bio- 

 logic host to emphasize that the investigator examine and evaluate the specific diet 

 being offered to his mice as a part of the entire experimental design rather than as a 

 casual consideration or afterthought. 291, 292, 1160 



Bedding and other environmental factors. — The bedding material selected should meet 

 the demands of good husbandry. These include the ability to absorb the moisture 

 of body wastes between changes of bedding. A highly absorbent material may be un- 

 desirable for breeding mice, since such material clings to newborn and very young animals 

 with a resultant dehydrating effect. In breeding cages, the bedding should provide 

 material for a nest which can easily be removed from cages when they are cleaned. 

 Some types of bedding such as baked, pulverized, or powdered clay, ground corn cobs, 

 or ground sugar cane are rather difficult to remove from cages after use and are often 

 found to be too absorbent. They also tend to clog drains and filters in automatic 

 cage-washing equipment because of the difficulty in removing all of the material before 

 washing. However, they have an advantage in being highly absorbent and hence 

 lengthen the interval between necessary cleaning. They may therefore be suitable for 

 certain types of experiments. 



One of the most satisfactory bedding materials is dried wood shavings. These 

 may be procured baled or in paper bags and are composed of a variety of woods. 

 The shavings should be fine and contain no large, coarse particles. Kiln-dried soft 

 wood such as pine makes the best shavings for bedding. Such wood shavings are 

 absorbent and make excellent nesting material for breeding mice. Shavings from 

 aromatic woods such as cedar have some suppressive value for ectoparasites, but on the 

 other hand their potential for irritating the skin and possible carcinogenicity are factors 

 to be considered. Since bedding material comes in most intimate contact with mice, 

 such factors must be weighed carefully. 



It is possible to keep mice on wire floors during experiments. These should be 

 of the hardware cloth type with \- or f-inch mesh, depending on the size and age of the 

 mice to be suspended. These floors should be raised at least f inch above a pan 

 containing absorbent material. 



The acceptable range in temperatures of a room in which mice are maintained is 

 + 2° F. level. The most satisfactory temperature is usually between 70 and 75 degrees 

 Fahrenheit. Mice withstand quite low and sometimes quite high (90° F.) temperatures 

 but our experience indicates that for peak breeding efficiency a temperature of 

 72° F. is a good one. Temperatures should be maintained at a constant level the year 

 round. Changes of air in our mouse rooms are maintained at a level of 6-7 changes 

 per hour level; many breeders use as many as 10-12 changes of air per hour. The 

 number of changes is of course determined by the number of animals kept in a given 

 room (each mouse contributes an average of 0.6 B.T.U. /hour/21 gram mouse from 

 body heat) and by the desired temperature. The ventilation system should be de- 

 signed to provide the necessary number of air changes in a manner free of drafts 

 directly on cages. A system designed for laboratories or schoolrooms is not necessarily 



