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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
• Study II (CD-I mice): Population density of two animals per cage (Trials 3 and 4): 
Relative humidity: Micro environmental RH in microisolator cages averaged 13 
percent higher than the room RH levels. 
Ammonia: All cages accumulated less than 5 ppm at day 8. There were no significant 
sex differences or significant differences in cages with replaced damaged filters in any 
of the parameters measured in either of the two studies. Air velocity across each cage 
and shelf of the rack was 0 to 0.65 m/second. The outermost cages were subject to the 
highest air velocity. 
• Study 3 (Strain/stock comparison): 
Temperature: The CD-I cages, DBA cages, and B ALB/c cages measured 23.5 to 
23.6 °C, which were not significantly different. 
Relative humidity: With average humidities measured at CD- 1 cage (82.9 percent), 
DBA cage (86.3 percent ), and BALB/c cage (79.0 percent ), only the BALB/c cages 
had significantly lower humidities than the DBA cages. For four mice housed in 
microisolator cages Ammonia time period averages (day 7) were CD-I = 149.5 ppm, 
DBA = 214.2 ppm, and BALB/c = 21.1 ppm. 
J.J. Hasenau, R.B. Baggs, and A.L. Kraus: Microenvironments in Microisolation Cages Using 
BALB/C And CD-I Mice , 1993, Contemp. Topics Lab. Anim. Sci., 32(1)11-16, 32(2)58-61; B.F. 
Coming, and N.S. Lipman: A Comparison of Rodent Caging Systems Based on 
Microenvironmental Parameters, 1991, Lab. Anim. Sci., 40:498-508; N.L. Sato, And M. Fukui: 
Dehumidification of Ventilation Air in a Barrier Maintenance System for Laboratory Animals, 
1989, Lab. Anim. Sci., 39:448-450; D. Wu, G.N. Joiner, and A.R. McFarland: A Forced-Air 
Ventilation System for Rodent Cages, 1985, Lab. Anim. Sci., 35:499-504; Gamble, M. R., and G. 
Clough: Ammonia Build-Up in Animal Boxes and its Effect on Rat Tracheal Epithelium, 1976, 
Lab. Anim. Sci. (London), 10:93-104. 
It was shown that ammonia is produced in greater amounts under conditions of high 
humidity. Desiccation was shown to be helpful in the prevention of ammonia and 
humidity accumulation as urease-producing bacteria grow less efficiently in the presence 
of reduced humidity. Lowering the macroenvironmental relative humidity levels and 
providing dehumidified air have been suggested as methods for preventing the elevation 
of humidity observed in barrier caging systems. 
C.M. Collins and S.E.F. D'Orazio: Bacterial Ureases-Structure, Regulation Of Expression and 
Role in Pathogenesis, 1993, Mol. Microbiol, 9:907-913; M. Dixon: D- Aspartate Oxidase, 1970, 
