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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
• Room air exchange rate, air velocity approaching the cage, number of returns and 
diffusers, and diffuser type did not significantly influence cage conditions and 
uniformity in cage conditions. 
Gwen C. Choi, Jennifer S. McQuinn, Brenda L. Jennings, Daniel J. Hassett, and Scott E. 
Michaels: Effect of Population Size on Humidity and Ammonia Levels in Individually Ventilated 
Microisolation Rodent Caging , 1994, Contemp. Topics Lab. Anim. Sci., 33:77-81. 
A study was undertaken to determine the effect of population size on the buildup of 
ammonia and humidity in individually ventilated microisolation cages over time as 
compared with static microisolation cages. Ammonia and relative humidity 
measurements were taken daily from sterilized, pressurized, individually ventilated 
microisolation cages and sterilized, static microisolation cages containing one to four, 24 
to 26 gram female Crl: CF-1 BR mice per cage. The effect of population size was 
evaluated over a 32-day period in the ventilated cages and over a 10-day period in the 
static cages. The bedding in each cage was 140 grams (360 cm 3 ) of combination 1/4-in 
and 1/8-in. No detectable levels of ammonia were present in any of the ventilated cages 
throughout the duration of the study. Ammonia was detected after eight days in the static 
microisolation cages containing three or four mice. Relative humidity levels in ventilated 
cages were not significantly different than room relative humidity levels indicating that 
the ventilation provided to the microisolation cages was effective in controlling intracage 
humidity. Relative humidity levels in static microisolation cages were significantly higher 
than room humidity levels, and a significant increase in relative humidity with increasing 
population density was observed. The complete lack of detectable ammonia levels in the 
ventilated cages and the low levels of ammonia detected in the static cages may have 
been influenced by the stock of animal studied, the autoclaving of the bedding, and the 
differences in ventilation rates of the two caging types. 
• The intracage relative humidity was approximately 23 percent to 36 percent higher 
than the room relative humidity depending on cage population density. 
• No ammonia was detected during the study period in cages containing one or two 
mice. Ammonia was detected after eight days in cages containing three or four mice. 
On days 9 and 10, the contrast of ammonia production between low population 
density (one or two mice/cage) and high population density (three or four mice per 
cage) was statistically significant. 
M.J. Huerkamp and N.D.M. Lehner: Comparative Effects of Forced-Air, Individual Cage 
Ventilation on an Absorbent Bedding Additive in Mouse Isolator Cage Microenvironment, 1994, 
Contemp. Topics Lab. Anim. Sci., 33(2)58-61; J.J. Hasenau, R.B. Baggs, and A.L. Kraus: 
Microenvironments in Microisolation Cages Using B ALB/C and CD-I Mice, 1993, Contemp. 
Topics Lab. Anim. Sci. ,32(1)1 1-16, 32(2)58-61; G.R. Gale and A.B. Smith: Ureolytic and 
